Learning statistics with R: A tutorial for psychology students and other beginners
(Version 0.6)
Fernando Millan Villalobos
April 2021
1 Notes
This report was generated on 2021-07-27 15:00:49. R version: 4.1.0 on x86_64-pc-linux-gnu. For this report, CRAN packages as of 2021-01-01 were used.
…
1.1 R-Script & data
The preprocessing and analysis of the data was conducted in the R project for statistical computing. The RMarkdown script used to generate this document and all the resulting data can be downloaded under this link. Through executing main.Rmd, the herein described process can be reproduced and this document can be generated. In the course of this, data from the folder input will be processed and results will be written to output. The html on-line version of the analysis can be accessed through this link.
1.2 GitHub
The code for the herein described process can also be freely downloaded from https://github.com/fernandomillanvillalobos/rddj-template.
1.3 License
…
1.4 Data description of output files
1.4.0.1 abc.csv (Example)
| Attribute | Type | Description |
|---|---|---|
| a | Numeric | … |
| b | Numeric | … |
| c | Numeric | … |
1.4.0.2 xyz.csv
…
2 Set up
## [1] "package package:rstudioapi detached"
## [1] "package package:knitr detached"2.1 Define packages
# from https://mran.revolutionanalytics.com/web/packages/\
# checkpoint/vignettes/using-checkpoint-with-knitr.html
# if you don't need a package, remove it from here (commenting not sufficient)
# tidyverse: see https://blog.rstudio.org/2016/09/15/tidyverse-1-0-0/
cat("
library(rstudioapi)
library(tidyverse, warn.conflicts = FALSE) # ggplot2, dplyr, tidyr, readr, purrr, tibble, magrittr, readxl
library(scales) # scales for ggplot2
library(jsonlite) # json
library(lintr) # code linting
library(sf) # spatial data handling
library(rmarkdown)
library(data.table)
library(cowplot) # theme
library(extrafont)
library(waldo) # compare
library(psych) # some useful funs
library(ggrepel) # text labels
library(skimr) # data quality
library(lsr) # book package
library(vcd)
library(sciplot)
library(gplots)
library(car) # statistics tests
library(lmtest) # more statistics tests
library(itns) # book itns
library(janitor)", # names
file = "manifest.R"
)2.2 Install packages
# if checkpoint is not yet installed, install it (for people using this
# system for the first time)
if (!require(checkpoint)) {
if (!require(devtools)) {
install.packages("devtools", repos = "http://cran.us.r-project.org")
require(devtools)
}
devtools::install_github("RevolutionAnalytics/checkpoint",
ref = "v0.3.2", # could be adapted later,
# as of now (beginning of July 2017
# this is the current release on CRAN)
repos = "http://cran.us.r-project.org"
)
require(checkpoint)
}
# nolint start
if (!dir.exists("~/.checkpoint")) {
dir.create("~/.checkpoint")
}
# nolint end
# install packages for the specified CRAN snapshot date
checkpoint(
snapshot_date = package_date,
project = path_to_wd,
verbose = T,
scanForPackages = T,
use.knitr = F,
R.version = r_version
)
rm(package_date)2.3 Load packages
source("manifest.R")
unlink("manifest.R")
sessionInfo()## R version 4.1.0 (2021-05-18)
## Platform: x86_64-pc-linux-gnu (64-bit)
## Running under: Ubuntu 20.04.2 LTS
##
## Matrix products: default
## BLAS: /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3
## LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/liblapack.so.3
##
## locale:
## [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
## [3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
## [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
## [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
## [9] LC_ADDRESS=C LC_TELEPHONE=C
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
##
## attached base packages:
## [1] grid stats graphics grDevices utils datasets methods
## [8] base
##
## other attached packages:
## [1] janitor_2.0.1 itns_0.1.0 lmtest_0.9-38 zoo_1.8-8
## [5] car_3.0-10 carData_3.0-4 gplots_3.1.1 sciplot_1.2-0
## [9] vcd_1.4-8 lsr_0.5 skimr_2.1.2 ggrepel_0.9.0
## [13] psych_2.0.12 waldo_0.2.5 extrafont_0.17 cowplot_1.1.1
## [17] data.table_1.13.6 rmarkdown_2.6 sf_0.9-6 lintr_2.0.1
## [21] jsonlite_1.7.2 scales_1.1.1 forcats_0.5.0 stringr_1.4.0
## [25] dplyr_1.0.2 purrr_0.3.4 readr_1.4.0 tidyr_1.1.2
## [29] tibble_3.0.4 ggplot2_3.3.3 tidyverse_1.3.0 rstudioapi_0.13
## [33] checkpoint_1.0.0
##
## loaded via a namespace (and not attached):
## [1] colorspace_2.0-0 ellipsis_0.3.1 class_7.3-19 rio_0.5.16
## [5] rprojroot_2.0.2 snakecase_0.11.0 base64enc_0.1-3 fs_1.5.0
## [9] remotes_2.4.0 lubridate_1.7.9.2 xml2_1.3.2 mnormt_2.0.2
## [13] knitr_1.30 broom_0.7.3 Rttf2pt1_1.3.8 dbplyr_2.0.0
## [17] compiler_4.1.0 httr_1.4.2 backports_1.2.1 assertthat_0.2.1
## [21] lazyeval_0.2.2 cli_2.5.0 htmltools_0.5.0 tools_4.1.0
## [25] gtable_0.3.0 glue_1.4.2 Rcpp_1.0.5 cellranger_1.1.0
## [29] vctrs_0.3.6 nlme_3.1-152 extrafontdb_1.0 xfun_0.19
## [33] ps_1.5.0 openxlsx_4.2.3 rvest_0.3.6 lifecycle_1.0.0
## [37] gtools_3.8.2 MASS_7.3-54 hms_0.5.3 rex_1.2.0
## [41] parallel_4.1.0 yaml_2.2.1 curl_4.3 stringi_1.5.3
## [45] desc_1.3.0 e1071_1.7-4 caTools_1.18.0 cyclocomp_1.1.0
## [49] zip_2.2.0 repr_1.1.0 rlang_0.4.10 pkgconfig_2.0.3
## [53] bitops_1.0-6 evaluate_0.14 lattice_0.20-44 processx_3.5.2
## [57] tidyselect_1.1.0 magrittr_2.0.1 R6_2.5.0 generics_0.1.0
## [61] DBI_1.1.0 pillar_1.4.7 haven_2.3.1 foreign_0.8-81
## [65] withr_2.4.2 units_0.6-7 abind_1.4-5 modelr_0.1.8
## [69] crayon_1.3.4 KernSmooth_2.23-20 tmvnsim_1.0-2 readxl_1.3.1
## [73] callr_3.7.0 reprex_0.3.0 digest_0.6.27 classInt_0.4-3
## [77] munsell_0.5.02.4 Load additional scripts
# if you want to outsource logic to other script files, see README for
# further information
# Load all visualizations functions as separate scripts
knitr::read_chunk("scripts/dviz.supp.R")
source("scripts/dviz.supp.R")
knitr::read_chunk("scripts/themes.R")
source("scripts/themes.R")
knitr::read_chunk("scripts/plot_grid.R")
source("scripts/plot_grid.R")
knitr::read_chunk("scripts/align_legend.R")
source("scripts/align_legend.R")
knitr::read_chunk("scripts/label_log10.R")
source("scripts/label_log10.R")3 Programming
3.1 Loops
# the while loop
x <- 0
while (x < 1000) {
x <- x + 17
}
x## [1] 1003# the for loop
for (i in 1:3) {
print("hello")
}## [1] "hello"
## [1] "hello"
## [1] "hello"# a simple example
words <- c("it", "was", "the", "dirty", "end", "of", "winter")
for (w in words) {
w.length <- nchar(w)
W <- toupper(w)
msg <- paste(W, "has", w.length, "letters")
print(msg)
}## [1] "IT has 2 letters"
## [1] "WAS has 3 letters"
## [1] "THE has 3 letters"
## [1] "DIRTY has 5 letters"
## [1] "END has 3 letters"
## [1] "OF has 2 letters"
## [1] "WINTER has 6 letters"# a more complex example
# set up
month <- 0 # count the number of months
balance <- 300000 # initial mortgage balance
payments <- 1600 # monthly payments
interest <- 0.05 # 5% interest rate per year
total.paid <- 0 # track what you've paid the bank
# convert annual interest to a monthly multiplier
monthly.multiplier <- (1 + interest)^(1 / 12)
# keep looping until the loan is paid off...
while (balance > 0) {
# do the calculations for this month
month <- month + 1 # one more month
balance <- balance * monthly.multiplier # add the interest
balance <- balance - payments # make the payments
total.paid <- total.paid + payments # track the total paid
# print the results on screen
cat("month", month, ": balance", round(balance), "\n")
} # end of loop## month 1 : balance 299622
## month 2 : balance 299243
## month 3 : balance 298862
## month 4 : balance 298480
## month 5 : balance 298096
## month 6 : balance 297710
## month 7 : balance 297323
## month 8 : balance 296934
## month 9 : balance 296544
## month 10 : balance 296152
## month 11 : balance 295759
## month 12 : balance 295364
## month 13 : balance 294967
## month 14 : balance 294569
## month 15 : balance 294169
## month 16 : balance 293768
## month 17 : balance 293364
## month 18 : balance 292960
## month 19 : balance 292553
## month 20 : balance 292145
## month 21 : balance 291735
## month 22 : balance 291324
## month 23 : balance 290911
## month 24 : balance 290496
## month 25 : balance 290079
## month 26 : balance 289661
## month 27 : balance 289241
## month 28 : balance 288820
## month 29 : balance 288396
## month 30 : balance 287971
## month 31 : balance 287545
## month 32 : balance 287116
## month 33 : balance 286686
## month 34 : balance 286254
## month 35 : balance 285820
## month 36 : balance 285385
## month 37 : balance 284947
## month 38 : balance 284508
## month 39 : balance 284067
## month 40 : balance 283625
## month 41 : balance 283180
## month 42 : balance 282734
## month 43 : balance 282286
## month 44 : balance 281836
## month 45 : balance 281384
## month 46 : balance 280930
## month 47 : balance 280475
## month 48 : balance 280018
## month 49 : balance 279559
## month 50 : balance 279098
## month 51 : balance 278635
## month 52 : balance 278170
## month 53 : balance 277703
## month 54 : balance 277234
## month 55 : balance 276764
## month 56 : balance 276292
## month 57 : balance 275817
## month 58 : balance 275341
## month 59 : balance 274863
## month 60 : balance 274382
## month 61 : balance 273900
## month 62 : balance 273416
## month 63 : balance 272930
## month 64 : balance 272442
## month 65 : balance 271952
## month 66 : balance 271460
## month 67 : balance 270966
## month 68 : balance 270470
## month 69 : balance 269972
## month 70 : balance 269472
## month 71 : balance 268970
## month 72 : balance 268465
## month 73 : balance 267959
## month 74 : balance 267451
## month 75 : balance 266941
## month 76 : balance 266428
## month 77 : balance 265914
## month 78 : balance 265397
## month 79 : balance 264878
## month 80 : balance 264357
## month 81 : balance 263834
## month 82 : balance 263309
## month 83 : balance 262782
## month 84 : balance 262253
## month 85 : balance 261721
## month 86 : balance 261187
## month 87 : balance 260651
## month 88 : balance 260113
## month 89 : balance 259573
## month 90 : balance 259031
## month 91 : balance 258486
## month 92 : balance 257939
## month 93 : balance 257390
## month 94 : balance 256839
## month 95 : balance 256285
## month 96 : balance 255729
## month 97 : balance 255171
## month 98 : balance 254611
## month 99 : balance 254048
## month 100 : balance 253483
## month 101 : balance 252916
## month 102 : balance 252346
## month 103 : balance 251774
## month 104 : balance 251200
## month 105 : balance 250623
## month 106 : balance 250044
## month 107 : balance 249463
## month 108 : balance 248879
## month 109 : balance 248293
## month 110 : balance 247705
## month 111 : balance 247114
## month 112 : balance 246521
## month 113 : balance 245925
## month 114 : balance 245327
## month 115 : balance 244727
## month 116 : balance 244124
## month 117 : balance 243518
## month 118 : balance 242911
## month 119 : balance 242300
## month 120 : balance 241687
## month 121 : balance 241072
## month 122 : balance 240454
## month 123 : balance 239834
## month 124 : balance 239211
## month 125 : balance 238585
## month 126 : balance 237958
## month 127 : balance 237327
## month 128 : balance 236694
## month 129 : balance 236058
## month 130 : balance 235420
## month 131 : balance 234779
## month 132 : balance 234136
## month 133 : balance 233489
## month 134 : balance 232841
## month 135 : balance 232189
## month 136 : balance 231535
## month 137 : balance 230879
## month 138 : balance 230219
## month 139 : balance 229557
## month 140 : balance 228892
## month 141 : balance 228225
## month 142 : balance 227555
## month 143 : balance 226882
## month 144 : balance 226206
## month 145 : balance 225528
## month 146 : balance 224847
## month 147 : balance 224163
## month 148 : balance 223476
## month 149 : balance 222786
## month 150 : balance 222094
## month 151 : balance 221399
## month 152 : balance 220701
## month 153 : balance 220000
## month 154 : balance 219296
## month 155 : balance 218590
## month 156 : balance 217880
## month 157 : balance 217168
## month 158 : balance 216453
## month 159 : balance 215735
## month 160 : balance 215014
## month 161 : balance 214290
## month 162 : balance 213563
## month 163 : balance 212833
## month 164 : balance 212100
## month 165 : balance 211364
## month 166 : balance 210625
## month 167 : balance 209883
## month 168 : balance 209138
## month 169 : balance 208390
## month 170 : balance 207639
## month 171 : balance 206885
## month 172 : balance 206128
## month 173 : balance 205368
## month 174 : balance 204605
## month 175 : balance 203838
## month 176 : balance 203069
## month 177 : balance 202296
## month 178 : balance 201520
## month 179 : balance 200741
## month 180 : balance 199959
## month 181 : balance 199174
## month 182 : balance 198385
## month 183 : balance 197593
## month 184 : balance 196798
## month 185 : balance 196000
## month 186 : balance 195199
## month 187 : balance 194394
## month 188 : balance 193586
## month 189 : balance 192775
## month 190 : balance 191960
## month 191 : balance 191142
## month 192 : balance 190321
## month 193 : balance 189496
## month 194 : balance 188668
## month 195 : balance 187837
## month 196 : balance 187002
## month 197 : balance 186164
## month 198 : balance 185323
## month 199 : balance 184478
## month 200 : balance 183629
## month 201 : balance 182777
## month 202 : balance 181922
## month 203 : balance 181063
## month 204 : balance 180201
## month 205 : balance 179335
## month 206 : balance 178466
## month 207 : balance 177593
## month 208 : balance 176716
## month 209 : balance 175836
## month 210 : balance 174953
## month 211 : balance 174065
## month 212 : balance 173175
## month 213 : balance 172280
## month 214 : balance 171382
## month 215 : balance 170480
## month 216 : balance 169575
## month 217 : balance 168666
## month 218 : balance 167753
## month 219 : balance 166836
## month 220 : balance 165916
## month 221 : balance 164992
## month 222 : balance 164064
## month 223 : balance 163133
## month 224 : balance 162197
## month 225 : balance 161258
## month 226 : balance 160315
## month 227 : balance 159368
## month 228 : balance 158417
## month 229 : balance 157463
## month 230 : balance 156504
## month 231 : balance 155542
## month 232 : balance 154576
## month 233 : balance 153605
## month 234 : balance 152631
## month 235 : balance 151653
## month 236 : balance 150671
## month 237 : balance 149685
## month 238 : balance 148695
## month 239 : balance 147700
## month 240 : balance 146702
## month 241 : balance 145700
## month 242 : balance 144693
## month 243 : balance 143683
## month 244 : balance 142668
## month 245 : balance 141650
## month 246 : balance 140627
## month 247 : balance 139600
## month 248 : balance 138568
## month 249 : balance 137533
## month 250 : balance 136493
## month 251 : balance 135449
## month 252 : balance 134401
## month 253 : balance 133349
## month 254 : balance 132292
## month 255 : balance 131231
## month 256 : balance 130166
## month 257 : balance 129096
## month 258 : balance 128022
## month 259 : balance 126943
## month 260 : balance 125861
## month 261 : balance 124773
## month 262 : balance 123682
## month 263 : balance 122586
## month 264 : balance 121485
## month 265 : balance 120380
## month 266 : balance 119270
## month 267 : balance 118156
## month 268 : balance 117038
## month 269 : balance 115915
## month 270 : balance 114787
## month 271 : balance 113654
## month 272 : balance 112518
## month 273 : balance 111376
## month 274 : balance 110230
## month 275 : balance 109079
## month 276 : balance 107923
## month 277 : balance 106763
## month 278 : balance 105598
## month 279 : balance 104428
## month 280 : balance 103254
## month 281 : balance 102074
## month 282 : balance 100890
## month 283 : balance 99701
## month 284 : balance 98507
## month 285 : balance 97309
## month 286 : balance 96105
## month 287 : balance 94897
## month 288 : balance 93683
## month 289 : balance 92465
## month 290 : balance 91242
## month 291 : balance 90013
## month 292 : balance 88780
## month 293 : balance 87542
## month 294 : balance 86298
## month 295 : balance 85050
## month 296 : balance 83797
## month 297 : balance 82538
## month 298 : balance 81274
## month 299 : balance 80005
## month 300 : balance 78731
## month 301 : balance 77452
## month 302 : balance 76168
## month 303 : balance 74878
## month 304 : balance 73583
## month 305 : balance 72283
## month 306 : balance 70977
## month 307 : balance 69666
## month 308 : balance 68350
## month 309 : balance 67029
## month 310 : balance 65702
## month 311 : balance 64369
## month 312 : balance 63032
## month 313 : balance 61688
## month 314 : balance 60340
## month 315 : balance 58986
## month 316 : balance 57626
## month 317 : balance 56261
## month 318 : balance 54890
## month 319 : balance 53514
## month 320 : balance 52132
## month 321 : balance 50744
## month 322 : balance 49351
## month 323 : balance 47952
## month 324 : balance 46547
## month 325 : balance 45137
## month 326 : balance 43721
## month 327 : balance 42299
## month 328 : balance 40871
## month 329 : balance 39438
## month 330 : balance 37998
## month 331 : balance 36553
## month 332 : balance 35102
## month 333 : balance 33645
## month 334 : balance 32182
## month 335 : balance 30713
## month 336 : balance 29238
## month 337 : balance 27758
## month 338 : balance 26271
## month 339 : balance 24778
## month 340 : balance 23279
## month 341 : balance 21773
## month 342 : balance 20262
## month 343 : balance 18745
## month 344 : balance 17221
## month 345 : balance 15691
## month 346 : balance 14155
## month 347 : balance 12613
## month 348 : balance 11064
## month 349 : balance 9509
## month 350 : balance 7948
## month 351 : balance 6380
## month 352 : balance 4806
## month 353 : balance 3226
## month 354 : balance 1639
## month 355 : balance 46
## month 356 : balance -1554# print the total payments at the end
cat("total payments made", total.paid, "\n")## total payments made 5696003.2 Conditional statements
# find out what day it is...
today <- Sys.Date() # pull the date from the system clock
day <- weekdays(today) # what day of the week it is_
# now make a choice depending on the day...
if (day == "Monday") {
print("I don't like Mondays")
} else {
print("I'm a happy little automaton")
}## [1] "I'm a happy little automaton"3.3 Functions
A formal argument can be a symbol (i.e. a variable name such as x or y), a statement of the form symbol = expression (e.g. pch=16) or the special formal argument … (triple dot).
# a simple function
quadruple <- function(x) {
y <- x * 4
return(y)
}
quadruple(3)## [1] 12# another simple function with two arguments
pow <- function(x, y = 1) { # setting a default value for args
out <- x^y # raise x to the power y
return(out)
}
pow(3, 2)## [1] 9# using the ... argument
doubleMax <- function(...) {
max.val <- max(...) # find the largest value in ...
out <- 2 * max.val # double it
return(out)
}
doubleMax(4, 6, 9)## [1] 183.4 Implicit loops
# sapply()
words <- c("along", "the", "loom", "of", "the", "land")
sapply(words, FUN = nchar)## along the loom of the land
## 5 3 4 2 3 4# tapply()
gender <- c("male", "male", "female", "female", "male")
age <- c(10, 12, 9, 11, 13)
# loop over all values that appear in the INDEX grouping variable
tapply(age, INDEX = gender, FUN = mean)## female male
## 10.00000 11.66667# by
by(age, INDICES = gender, FUN = mean) # does the same as tapply## gender: female
## [1] 10
## ------------------------------------------------------------
## gender: male
## [1] 11.666674 Descriptive statistics
4.1 Measures of central tendency
# Load data
load("~/lsr/lsr/analysis/input/aflsmall.Rdata")
table(afl.finalists)## afl.finalists
## Adelaide Brisbane Carlton Collingwood
## 26 25 26 28
## Essendon Fitzroy Fremantle Geelong
## 32 0 6 39
## Hawthorn Melbourne North Melbourne Port Adelaide
## 27 28 28 17
## Richmond St Kilda Sydney West Coast
## 6 24 26 38
## Western Bulldogs
## 24# calculate the mode
m <- modeOf(afl.finalists)
cat("The mode of the dataset is", m, "\n")## The mode of the dataset is Geelong# calculate the modal frequency
max <- maxFreq(afl.finalists)
cat("The modal frequency of the dataset is", max, "\n")## The modal frequency of the dataset is 394.2 Measures of variability
# calculate quantiles
quantile(afl.margins, probs = .5)## 50%
## 30.5quantile(afl.margins, probs = c(.25, .75))## 25% 75%
## 12.75 50.50# calculate IQR
i <- IQR(afl.margins)
cat("IQR is", i, "\n")## IQR is 37.75# calculate the mean absolute deviation (AAD)
a <- aad(afl.margins[1:5])
cat("The mean absolute deviation (AAD) is", a, "\n")## The mean absolute deviation (AAD) is 15.52# calculate variance (also called mean square deviation)
v <- var(afl.margins[1:5])
cat("The variance is", v, "\n")## The variance is 405.8# calculate standard deviation (also called root mean squared deviation)
s <- sd(afl.margins)
cat("The standard deviation is", s, "\n")## The standard deviation is 26.07364# calculate median absolute deviation (MAD)
m <- mad(afl.margins, constant = 1)
cat("The median absolute deviation (MAD) is", m, "\n")## The median absolute deviation (MAD) is 19.5# calculate skewness
sk <- skew(afl.margins)
cat("The skewness is", sk, "\n")## The skewness is 0.7671555# calculate kurtosis
k <- kurtosi(afl.margins)
cat("The kurtosis is", k, "\n")## The kurtosis is 0.029626334.3 Overall data summary
# load data
load("~/lsr/lsr/analysis/input/clinicaltrial.Rdata")
# for numeric variables
summary(afl.margins)## Min. 1st Qu. Median Mean 3rd Qu. Max.
## 0.00 12.75 30.50 35.30 50.50 116.00# for nominal (factor) variables
summary(afl.finalists)## Adelaide Brisbane Carlton Collingwood
## 26 25 26 28
## Essendon Fitzroy Fremantle Geelong
## 32 0 6 39
## Hawthorn Melbourne North Melbourne Port Adelaide
## 27 28 28 17
## Richmond St Kilda Sydney West Coast
## 6 24 26 38
## Western Bulldogs
## 24# for data frames
describe(x = clin.trial)| vars | n | mean | sd | median | trimmed | mad | min | max | range | skew | kurtosis | se | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| drug* | 1 | 18 | 2.0000000 | 0.8401681 | 2.00 | 2.000 | 1.48260 | 1.0 | 3.0 | 2.0 | 0.0000000 | -1.662037 | 0.1980295 |
| therapy* | 2 | 18 | 1.5000000 | 0.5144958 | 1.50 | 1.500 | 0.74130 | 1.0 | 2.0 | 1.0 | 0.0000000 | -2.108025 | 0.1212678 |
| mood.gain | 3 | 18 | 0.8833333 | 0.5338539 | 0.85 | 0.875 | 0.66717 | 0.1 | 1.8 | 1.7 | 0.1333981 | -1.439739 | 0.1258306 |
# broken down by grouping variable
describeBy(clin.trial, group = clin.trial$therapy)##
## Descriptive statistics by group
## group: no.therapy
## vars n mean sd median trimmed mad min max range skew kurtosis se
## drug* 1 9 2.00 0.87 2.0 2.00 1.48 1.0 3.0 2.0 0.00 -1.81 0.29
## therapy* 2 9 1.00 0.00 1.0 1.00 0.00 1.0 1.0 0.0 NaN NaN 0.00
## mood.gain 3 9 0.72 0.59 0.5 0.72 0.44 0.1 1.7 1.6 0.51 -1.59 0.20
## ------------------------------------------------------------
## group: CBT
## vars n mean sd median trimmed mad min max range skew kurtosis
## drug* 1 9 2.00 0.87 2.0 2.00 1.48 1.0 3.0 2.0 0.00 -1.81
## therapy* 2 9 2.00 0.00 2.0 2.00 0.00 2.0 2.0 0.0 NaN NaN
## mood.gain 3 9 1.04 0.45 1.1 1.04 0.44 0.3 1.8 1.5 -0.03 -1.12
## se
## drug* 0.29
## therapy* 0.00
## mood.gain 0.15by(clin.trial, INDICES = clin.trial$therapy, FUN = describe)## clin.trial$therapy: no.therapy
## vars n mean sd median trimmed mad min max range skew kurtosis se
## drug* 1 9 2.00 0.87 2.0 2.00 1.48 1.0 3.0 2.0 0.00 -1.81 0.29
## therapy* 2 9 1.00 0.00 1.0 1.00 0.00 1.0 1.0 0.0 NaN NaN 0.00
## mood.gain 3 9 0.72 0.59 0.5 0.72 0.44 0.1 1.7 1.6 0.51 -1.59 0.20
## ------------------------------------------------------------
## clin.trial$therapy: CBT
## vars n mean sd median trimmed mad min max range skew kurtosis
## drug* 1 9 2.00 0.87 2.0 2.00 1.48 1.0 3.0 2.0 0.00 -1.81
## therapy* 2 9 2.00 0.00 2.0 2.00 0.00 2.0 2.0 0.0 NaN NaN
## mood.gain 3 9 1.04 0.45 1.1 1.04 0.44 0.3 1.8 1.5 -0.03 -1.12
## se
## drug* 0.29
## therapy* 0.00
## mood.gain 0.15by(clin.trial, INDICES = clin.trial$therapy, FUN = summary)## clin.trial$therapy: no.therapy
## drug therapy mood.gain
## placebo :3 no.therapy:9 Min. :0.1000
## anxifree:3 CBT :0 1st Qu.:0.3000
## joyzepam:3 Median :0.5000
## Mean :0.7222
## 3rd Qu.:1.3000
## Max. :1.7000
## ------------------------------------------------------------
## clin.trial$therapy: CBT
## drug therapy mood.gain
## placebo :3 no.therapy:0 Min. :0.300
## anxifree:3 CBT :9 1st Qu.:0.800
## joyzepam:3 Median :1.100
## Mean :1.044
## 3rd Qu.:1.300
## Max. :1.800aggregate(mood.gain ~ drug + therapy, data = clin.trial, FUN = mean)| drug | therapy | mood.gain |
|---|---|---|
| placebo | no.therapy | 0.300000 |
| anxifree | no.therapy | 0.400000 |
| joyzepam | no.therapy | 1.466667 |
| placebo | CBT | 0.600000 |
| anxifree | CBT | 1.033333 |
| joyzepam | CBT | 1.500000 |
4.4 Correlations
# load data
load("~/lsr/lsr/analysis/input/parenthood.Rdata")
hist(parenthood$dan.grump)
hist(parenthood$dan.sleep)
hist(parenthood$baby.sleep)
plot(x = parenthood$dan.sleep, y = parenthood$dan.grump)
plot(x = parenthood$baby.sleep, y = parenthood$dan.grump)
# calculate correlations (the Pearson's correlation)
cor(x = parenthood$dan.sleep, y = parenthood$dan.grump)## [1] -0.903384cor(parenthood)## dan.sleep baby.sleep dan.grump day
## dan.sleep 1.00000000 0.62794934 -0.90338404 -0.09840768
## baby.sleep 0.62794934 1.00000000 -0.56596373 -0.01043394
## dan.grump -0.90338404 -0.56596373 1.00000000 0.07647926
## day -0.09840768 -0.01043394 0.07647926 1.00000000# load data
load("~/lsr/lsr/analysis/input/effort.Rdata")
# calculate correlations (the Spearmans's correlation)
hours_rank <- rank(effort$hours)
grade_rank <- rank(effort$grade)
cor(hours_rank, grade_rank)## [1] 1# or
cor(effort$hours, effort$grade, method = "spearman")## [1] 1# calculate correlations getting rid of all non-numeric variables
# # load data
load("~/lsr/lsr/analysis/input/work.Rdata")
lsr::correlate(work)##
## CORRELATIONS
## ============
## - correlation type: pearson
## - correlations shown only when both variables are numeric
##
## hours tasks pay day weekday week day.type
## hours . 0.800 0.760 -0.049 . 0.018 .
## tasks 0.800 . 0.720 -0.072 . -0.013 .
## pay 0.760 0.720 . 0.137 . 0.196 .
## day -0.049 -0.072 0.137 . . 0.990 .
## weekday . . . . . . .
## week 0.018 -0.013 0.196 0.990 . . .
## day.type . . . . . . .lsr::correlate(work, corr.method = "spearman")##
## CORRELATIONS
## ============
## - correlation type: spearman
## - correlations shown only when both variables are numeric
##
## hours tasks pay day weekday week day.type
## hours . 0.805 0.745 -0.047 . 0.010 .
## tasks 0.805 . 0.730 -0.068 . -0.008 .
## pay 0.745 0.730 . 0.094 . 0.154 .
## day -0.047 -0.068 0.094 . . 0.990 .
## weekday . . . . . . .
## week 0.010 -0.008 0.154 0.990 . . .
## day.type . . . . . . .# look at the data
head(body_well)| sex | bodysat | wellbeing |
|---|---|---|
| female | 4.000000 | 1.0 |
| female | 2.428571 | 2.4 |
| female | 3.000000 | 2.3 |
| female | 3.000000 | 2.4 |
| female | 3.142857 | 2.8 |
| female | 2.428571 | 3.2 |
dplyr::glimpse(body_well)## Rows: 106
## Columns: 3
## $ sex <fct> female, female, female, female, female, female, female, fem…
## $ bodysat <dbl> 4.000000, 2.428571, 3.000000, 3.000000, 3.142857, 2.428571,…
## $ wellbeing <dbl> 1.0, 2.4, 2.3, 2.4, 2.8, 3.2, 3.4, 3.4, 3.6, 3.6, 3.8, 3.8,…plot(x = body_well$bodysat, y = body_well$wellbeing)
ggplot(body_well, aes(x = bodysat, y = wellbeing)) +
geom_point(shape = 21, fill = "deepskyblue4", stroke = .5, size = 3, alpha = .7) +
geom_smooth(method = "lm", se = FALSE) +
theme_cowplot()
# calculating Pearson's correlation coefficient
cor(body_well$bodysat, body_well$wellbeing, method = "spearman")## [1] 0.4726243lsr::correlate(x = body_well$bodysat, y = body_well$wellbeing, corr.method = "spearman")##
## CORRELATIONS
## ============
## - correlation type: spearman
## - correlations shown only when both variables are numeric
##
## y.var
## x.var 0.473# eyeballing r correlation coefficient
ggplot(body_well, aes(x = bodysat, y = wellbeing)) +
geom_point(shape = 21, fill = "deepskyblue4", stroke = .5, size = 3, alpha = .7) +
geom_vline(aes(xintercept = mean(bodysat)), size = .3, linetype = "dashed", color = "red") +
geom_hline(aes(yintercept = mean(wellbeing)), size = .3, linetype = "dashed", color = "red") +
theme_cowplot()
# look at the data
head(thomason1)| pre | post |
|---|---|
| 13 | 14 |
| 12 | 13 |
| 12 | 16 |
| 9 | 12 |
| 14 | 15 |
| 17 | 18 |
dplyr::glimpse(thomason1)## Rows: 12
## Columns: 2
## $ pre <dbl> 13, 12, 12, 9, 14, 17, 14, 9, 6, 7, 11, 15
## $ post <dbl> 14, 13, 16, 12, 15, 18, 13, 10, 10, 8, 14, 16plot(x = thomason1$pre, y = thomason1$post)
ggplot(thomason1, aes(x = pre, y = post)) +
geom_point(shape = 21, fill = "deepskyblue4", stroke = .5, size = 3, alpha = .7) +
scale_y_continuous(expand = c(0, 0), limits = c(0, 20), breaks = seq(0, 20, 2)) +
scale_x_continuous(expand = c(0, 0), limits = c(0, 18), breaks = seq(0, 18, 2)) +
geom_smooth(method = "lm", se = FALSE) +
theme_cowplot()
# calculating Pearson's correlation coefficient
cor(thomason1$pre, thomason1$post, method = "spearman")## [1] 0.8424792lsr::correlate(x = thomason1$pre, y = thomason1$post, corr.method = "spearman")##
## CORRELATIONS
## ============
## - correlation type: spearman
## - correlations shown only when both variables are numeric
##
## y.var
## x.var 0.842# eyeballing r correlation coefficient
ggplot(thomason1, aes(x = pre, y = post)) +
geom_point(shape = 21, fill = "deepskyblue4", stroke = .5, size = 3, alpha = .7) +
scale_y_continuous(expand = c(0, 0), limits = c(0, 20), breaks = seq(0, 20, 2)) +
scale_x_continuous(expand = c(0, 0), limits = c(0, 18), breaks = seq(0, 18, 2)) +
geom_vline(aes(xintercept = mean(pre)), size = .3, linetype = "dashed", color = "red") +
geom_hline(aes(yintercept = mean(post)), size = .3, linetype = "dashed", color = "red") +
theme_cowplot()
# look at the data
head(sleep_beauty)| nightly_sleep_hours | rated_attractiveness |
|---|---|
| 9.3 | 3.475840 |
| 11.5 | 3.813389 |
| 6.7 | 4.917097 |
| 9.3 | 5.000430 |
| 9.8 | 4.685868 |
| 7.9 | 4.249000 |
dplyr::glimpse(sleep_beauty)## Rows: 70
## Columns: 2
## $ nightly_sleep_hours <dbl> 9.3, 11.5, 6.7, 9.3, 9.8, 7.9, 8.0, 10.4, 3.7, 1…
## $ rated_attractiveness <dbl> 3.475840, 3.813389, 4.917097, 5.000430, 4.685868…# eyeballing r correlation coefficient
ggplot(sleep_beauty, aes(x = nightly_sleep_hours, y = rated_attractiveness)) +
geom_point(shape = 21, fill = "deepskyblue4", stroke = .5, size = 3, alpha = .7) +
geom_smooth(method = "lm", se = FALSE) +
scale_y_continuous(expand = c(0, 0), limits = c(0, 8), breaks = seq(0, 8, 1)) +
scale_x_continuous(expand = c(0, 0), limits = c(0, 14), breaks = seq(0, 14, 1)) +
geom_vline(aes(xintercept = mean(nightly_sleep_hours)), size = .3, linetype = "dashed", color = "red") +
geom_hline(aes(yintercept = mean(rated_attractiveness)), size = .3, linetype = "dashed", color = "red") +
theme_cowplot()
# calculating CI's for r
cor.test(x = sleep_beauty$nightly_sleep_hours, y = sleep_beauty$rated_attractiveness)##
## Pearson's product-moment correlation
##
## data: sleep_beauty$nightly_sleep_hours and sleep_beauty$rated_attractiveness
## t = -2.7175, df = 68, p-value = 0.008337
## alternative hypothesis: true correlation is not equal to 0
## 95 percent confidence interval:
## -0.51041935 -0.08420143
## sample estimates:
## cor
## -0.3129834.5 Handling missing values
# load data
load("~/lsr/lsr/analysis/input/parenthood2.Rdata")
# ignore all cases that have any missing values
cor(parenthood2, use = "complete.obs")## dan.sleep baby.sleep dan.grump day
## dan.sleep 1.00000000 0.6394985 -0.89951468 0.06132891
## baby.sleep 0.63949845 1.0000000 -0.58656066 0.14555814
## dan.grump -0.89951468 -0.5865607 1.00000000 -0.06816586
## day 0.06132891 0.1455581 -0.06816586 1.00000000# look at the variables when determining what to drop
cor(parenthood2, use = "pairwise.complete.obs")## dan.sleep baby.sleep dan.grump day
## dan.sleep 1.00000000 0.61472303 -0.903442442 -0.076796665
## baby.sleep 0.61472303 1.00000000 -0.567802669 0.058309485
## dan.grump -0.90344244 -0.56780267 1.000000000 0.005833399
## day -0.07679667 0.05830949 0.005833399 1.0000000004.6 Transforming or recoding a variable
# load data
load("~/lsr/lsr/analysis/input/likert.Rdata")
# make a data frame
df <- data.frame(likert.raw)
# recode the variable (+3 strong agree, 0 no opinion, -3 strong disagree)
df$likert.centred <- df$likert.raw - 4
# create a strength variable
df$opinion.strength <- abs(df$likert.centred)
# create a direction variable (all negative numbers converted to -1, all positives to 1 and zero stays 0)
df$opinion.dir <- sign(df$likert.centred)
df| likert.raw | likert.centred | opinion.strength | opinion.dir |
|---|---|---|---|
| 1 | -3 | 3 | -1 |
| 7 | 3 | 3 | 1 |
| 3 | -1 | 1 | -1 |
| 4 | 0 | 0 | 0 |
| 4 | 0 | 0 | 0 |
| 4 | 0 | 0 | 0 |
| 2 | -2 | 2 | -1 |
| 6 | 2 | 2 | 1 |
| 5 | 1 | 1 | 1 |
| 5 | 1 | 1 | 1 |
# cutting numeric variables into categories
age <- c(60, 58, 24, 26, 34, 42, 31, 30, 33, 2, 9)
age.breaks <- seq(from = 0, to = 60, by = 20)
age.labels <- c("young", "adult", "older")
age.group <- cut(x = age, breaks = age.breaks, labels = age.labels)
age.df <- data.frame(age, age.group)4.7 Subsetting
# load data
load("~/lsr/lsr/analysis/input/nightgarden.Rdata")
itng <- data.frame(speaker, utterance)
# using split
speech.by.char <- split(utterance, speaker)
speech.by.char## $`makka-pakka`
## [1] "pip" "pip" "onk" "onk"
##
## $tombliboo
## [1] "ee" "oo"
##
## $`upsy-daisy`
## [1] "pip" "pip" "onk" "onk"# pull grouping variables out of the list and into workspace
importList(speech.by.char, ask = FALSE)
# using subset
df <- subset(itng, subset = speaker == "makka-pakka", select = utterance)4.8 Sorting, flipping and merging data
# load data
load("~/lsr/lsr/analysis/input/nightgarden2.Rdata")
# sorting a data frame
sortFrame(garden, speaker, line)| speaker | utterance | line | |
|---|---|---|---|
| case.4 | makka-pakka | pip | 7 |
| case.5 | makka-pakka | onk | 9 |
| case.3 | tombliboo | ee | 5 |
| case.1 | upsy-daisy | pip | 1 |
| case.2 | upsy-daisy | pip | 2 |
# reverse order
sortFrame(garden, -speaker, line)| speaker | utterance | line | |
|---|---|---|---|
| case.1 | upsy-daisy | pip | 1 |
| case.2 | upsy-daisy | pip | 2 |
| case.3 | tombliboo | ee | 5 |
| case.4 | makka-pakka | pip | 7 |
| case.5 | makka-pakka | onk | 9 |
4.9 Working with text
# Shortening a string
animals <- c("cat", "dog", "kangaroo", "whale")
strtrim(animals, width = 3)## [1] "cat" "dog" "kan" "wha"substr(animals, start = 2, stop = 3)## [1] "at" "og" "an" "ha"# Paste strings together
paste("hello", "world")## [1] "hello world"paste0("hello", "world")## [1] "helloworld"paste("hello", "world", sep = ".")## [1] "hello.world"hw <- c("hello", "world")
ng <- c("nasty", "government")
paste(hw, ng)## [1] "hello nasty" "world government"paste(hw, ng, collapse = " ")## [1] "hello nasty world government"# Splitting strings
monkey <- "It was the best of times. It was the blurst of times."
monkey.1 <- strsplit(monkey, split = " ", fixed = T)
monkey.2 <- strsplit(monkey, split = ".", fixed = T)
# Making transformations
old.text <- "albmino"
chartr(old = "alb", new = "chu", old.text)## [1] "chumino"# Matching and substituting text
beers <- c("little creatures", "sierra nevada", "coopers pale")
grep(pattern = "er", beers, fixed = T, value = T)## [1] "sierra nevada" "coopers pale"gsub(pattern = "a", replacement = "BLAH", beers, fixed = T)## [1] "little creBLAHtures" "sierrBLAH nevBLAHdBLAH" "coopers pBLAHle"sub(pattern = "a", replacement = "BLAH", beers, fixed = T)## [1] "little creBLAHtures" "sierrBLAH nevada" "coopers pBLAHle"5 Inferential statistics
5.1 Introduction to probability
# Functions to draw plots to show probability distributions
# Parameters for plots
emphCol <- rgb(0, 0, 1)
colour <- TRUE
emphColLight <- rgb(.5, .5, 1)
emphGrey <- grey(.5)
# Function to produce a styled binomial plot
binomPlot <- function(n, p, ...) {
# probabilities of each outcome
out <- 0:n
prob <- dbinom(x = out, size = n, prob = p)
# plot
plot(
out, prob,
type = "h", lwd = 3, ylab = "Probability",
frame.plot = FALSE, col = ifelse(colour, emphCol, "black"), ...
)
}
binomPlot(40, 1 / 4, xlab = "Number of skulls observed")
# Function to plot a normal distribution
standardNormal <- function() {
# draw the plot
xval <- seq(-3, 3, .01)
yval <- dnorm(xval, 0, 1)
plot(xval, yval,
lwd = 3, ylab = "Probability Density", xlab = "Observed Value",
frame.plot = FALSE, col = ifelse(colour, emphCol, "black"), type = "l"
)
}
standardNormal()
# Function to plot the different probability distributions
variateRelations <- function() {
# generate the data
n <- 1000
normal.a <- rnorm(n)
normal.b <- rnorm(n)
normal.c <- rnorm(n)
chi.sq.3 <- (normal.a)^2 + (normal.b)^2 + (normal.c)^2
normal.d <- rnorm(n)
t.3 <- normal.d / sqrt(chi.sq.3 / 3)
chi.sq.20 <- rchisq(n, 20)
F.3.20 <- (chi.sq.3 / 3) / (chi.sq.20 / 20)
# histogram for the normal data
bw <- .25
hist(normal.a, seq(min(normal.a) - bw, max(normal.a) + bw, bw),
freq = FALSE, xlim = c(-4, 4),
col = ifelse(colour, emphColLight, emphGrey),
border = "white", ylim = c(0, .45), axes = FALSE,
xlab = "", ylab = "", main = "Simulated Normal Data",
font.main = 1
)
lines(x <- seq(-4, 4, .1), dnorm(x), lwd = 3, col = "black")
axis(1)
# histogram for the chi square data
bw <- .5
hist(chi.sq.3, seq(0, max(chi.sq.3) + bw, bw),
freq = FALSE, xlim = c(0, 16),
col = ifelse(colour, emphColLight, emphGrey),
border = "white", axes = FALSE, ylim = c(0, .25),
xlab = "", ylab = "", main = "Simulated Chi-Square Data",
font.main = 1
)
lines(x <- seq(0, 16, .1), dchisq(x, 3), lwd = 3, col = "black")
axis(1)
# histogram for the t data
bw <- .3
hist(t.3, seq(min(t.3) - bw, max(t.3) + bw, bw),
freq = FALSE, xlim = c(-5, 5),
col = ifelse(colour, emphColLight, emphGrey),
border = "white", axes = FALSE, ylim = c(0, .4),
xlab = "", ylab = "", main = "Simulated t Data",
font.main = 1
)
lines(x <- seq(-4, 4, .1), dt(x, 3), lwd = 3, col = "black")
axis(1)
# histogram for the F dist data
bw <- .2
hist(F.3.20, seq(0, max(F.3.20) + bw, bw),
freq = FALSE, xlim = c(0, 6),
col = ifelse(colour, emphColLight, emphGrey),
border = "white", axes = FALSE, ylim = c(0, .7),
xlab = "", ylab = "", main = "Simulated F Data",
font.main = 1
)
lines(x <- seq(0, 6, .01), df(x, 3, 20), lwd = 3, col = "black")
axis(1)
}
variateRelations()
# Plotting the sampling distribution of the mean with different sample sizes
samplingDistributions <- function() {
# Plots histograms of IQ samples and sampling distributions
plotSamples <- function(n, N) {
IQ <- rnorm(n, 100, 15 / sqrt(N))
hist(IQ,
breaks = seq(10, 180, 5), border = "white", freq = FALSE,
col = ifelse(colour, emphColLight, emphGrey),
xlab = "IQ Score", ylab = "", xlim = c(60, 140),
main = paste("Sample Size =", N), axes = FALSE,
font.main = 1, ylim = c(0, .07)
)
axis(1)
}
# population distribution
x <- 60:140
y <- dnorm(x, 100, 15)
# plot two different sample sizes
plotSamples(10000, 1)
lines(x, y, lwd = 2, col = "black", type = "l")
# plot two different sample sizes
plotSamples(1000, 2)
lines(x, y, lwd = 2, col = "black", type = "l")
# plot two different sample sizes
plotSamples(1000, 10)
lines(x, y, lwd = 2, col = "black", type = "l")
}
samplingDistributions()
5.2 Confidence interval (CI)
# computing the 2.5th and the 97.5th percentiles (95% CI) of the normal distribution
qnorm(p = c(.025, .975))## [1] -1.959964 1.959964# the 15th and 85th (70% CI)
qnorm(p = c(.15, .85))## [1] -1.036433 1.036433# calculating quantiles of the t distribution (95% CI)
qt(p = .975, df = 1000 - 1) # large sample## [1] 1.962341qt(p = .975, df = 10 - 1) # small sample## [1] 2.262157# calculating CI
# load data
load("~/lsr/lsr/analysis/input/afl24.Rdata")
ciMean(x = afl$attendance) # 95% CI (default)## 2.5% 97.5%
## [1,] 31597.32 32593.12ciMean(x = afl$attendance, conf = .99) # 99% CI (default)## 0.5% 99.5%
## [1,] 31440.77 32749.68# plotting CI
# using bargraph
bargraph.CI(
x.factor = year, # grouping variable
response = attendance, # outcome variable
data = afl, # data
ci.fun = ciMean, # name of the function to calculate CIs
xlab = "Year",
ylab = "Average Attendance"
)
# using lineplot
lineplot.CI(
x.factor = year, # grouping variable
response = attendance, # outcome variable
data = afl, # data
ci.fun = ciMean, # name of the function to calculate CIs
xlab = "Year",
ylab = "Average Attendance"
)
# using plotmeans
plotmeans(
formula = attendance ~ year,
data = afl,
n.label = FALSE
)
5.3 Categorical Data Analysis
# load data
load("input/randomness.Rdata")
load("input/chapek9.Rdata")
load("input/salem.Rdata")
load("input/agpp.Rdata")
#---------- The chi-squared goodnest-of-fit test ----------
observed <- table(cards$choice_1)
observed##
## clubs diamonds hearts spades
## 35 51 64 50# R mathematical version
probabilities <- c(clubs = .25, diamonds = .25, hearts = .25, spaces = .25)
N <- 200
expected <- N * probabilities # expected frequencies
expected## clubs diamonds hearts spaces
## 50 50 50 50# difference between null hypothesis expected and actual values
observed - expected##
## clubs diamonds hearts spades
## -15 1 14 0# squared that difference to get a collection of numbers that are big whenever the
# null hypothesis makes a bad prediction
(observed - expected)^2##
## clubs diamonds hearts spades
## 225 1 196 0# getting different error scores
(observed - expected)^2 / expected##
## clubs diamonds hearts spades
## 4.50 0.02 3.92 0.00# getting the goodness of fit statistic (X^2 or GOF)
sum((observed - expected)^2 / expected)## [1] 8.44# calculating the 95th percentile of a chi-squared distribution with k - 1 degrees of freedom
qchisq(p = .95, df = 3)## [1] 7.814728# getting the p-value
pchisq(q = 8.44, df = 3, lower.tail = F)## [1] 0.03774185# or
1 - pchisq(q = 8.44, df = 3)## [1] 0.03774185# all above calculations all at once
goodnessOfFitTest(cards$choice_1)##
## Chi-square test against specified probabilities
##
## Data variable: cards$choice_1
##
## Hypotheses:
## null: true probabilities are as specified
## alternative: true probabilities differ from those specified
##
## Descriptives:
## observed freq. expected freq. specified prob.
## clubs 35 50 0.25
## diamonds 51 50 0.25
## hearts 64 50 0.25
## spades 50 50 0.25
##
## Test results:
## X-squared statistic: 8.44
## degrees of freedom: 3
## p-value: 0.038# specifying a different null hypothesis
nullProbs <- c(clubs = .2, diamonds = .3, hearts = .3, spades = .2)
goodnessOfFitTest(cards$choice_1, p = nullProbs)##
## Chi-square test against specified probabilities
##
## Data variable: cards$choice_1
##
## Hypotheses:
## null: true probabilities are as specified
## alternative: true probabilities differ from those specified
##
## Descriptives:
## observed freq. expected freq. specified prob.
## clubs 35 40 0.2
## diamonds 51 60 0.3
## hearts 64 60 0.3
## spades 50 40 0.2
##
## Test results:
## X-squared statistic: 4.742
## degrees of freedom: 3
## p-value: 0.192# using chisq.test() for the goodness of fit test -> frequency table (observed)
chisq.test(observed)##
## Chi-squared test for given probabilities
##
## data: observed
## X-squared = 8.44, df = 3, p-value = 0.03774chisq.test(x = observed, p = c(clubs = .2, diamonds = .3, hearts = .3, spades = .2))##
## Chi-squared test for given probabilities
##
## data: observed
## X-squared = 4.7417, df = 3, p-value = 0.1917#---------- The chi-squared test of independence (or association) test ----------
# producing a contingency table
chapekFrequencies <- xtabs(~ choice + species, data = chapek9)
chapekFrequencies## species
## choice robot human
## puppy 13 15
## flower 30 13
## data 44 65chapekFrequenciesSum <- addmargins(chapekFrequencies, margin = c(1, 2), FUN = sum, quiet = T)
# running the test
associationTest(formula = ~ choice + species, data = chapek9)##
## Chi-square test of categorical association
##
## Variables: choice, species
##
## Hypotheses:
## null: variables are independent of one another
## alternative: some contingency exists between variables
##
## Observed contingency table:
## species
## choice robot human
## puppy 13 15
## flower 30 13
## data 44 65
##
## Expected contingency table under the null hypothesis:
## species
## choice robot human
## puppy 13.5 14.5
## flower 20.8 22.2
## data 52.7 56.3
##
## Test results:
## X-squared statistic: 10.722
## degrees of freedom: 2
## p-value: 0.005
##
## Other information:
## estimated effect size (Cramer's v): 0.244# using chisq.test() for a test of independence (assocition) -> cross-tabulation table (chapekFrequencies)
chisq.test(chapekFrequencies)##
## Pearson's Chi-squared test
##
## data: chapekFrequencies
## X-squared = 10.722, df = 2, p-value = 0.004697#---------- The Fisher exact test ----------
salem.tabs <- table(trial)
salem.tabs## on.fire
## happy FALSE TRUE
## FALSE 3 3
## TRUE 10 0# running the test
fisher.test(salem.tabs)##
## Fisher's Exact Test for Count Data
##
## data: salem.tabs
## p-value = 0.03571
## alternative hypothesis: true odds ratio is not equal to 1
## 95 percent confidence interval:
## 0.000000 1.202913
## sample estimates:
## odds ratio
## 0#---------- The McNemar test ----------
right.table <- xtabs(~ response_before + response_after, data = agpp)
right.table## response_after
## response_before no yes
## no 65 5
## yes 25 5# running the test
mcnemar.test(right.table)##
## McNemar's Chi-squared test with continuity correction
##
## data: right.table
## McNemar's chi-squared = 12.033, df = 1, p-value = 0.0005226cardChoices <- xtabs(~ choice_1 + choice_2, data = cards)
cardChoices## choice_2
## choice_1 clubs diamonds hearts spades
## clubs 10 9 10 6
## diamonds 20 4 13 14
## hearts 20 18 3 23
## spades 18 13 15 4# testing if there is a relation between rows and columns
chisq.test(cardChoices)##
## Pearson's Chi-squared test
##
## data: cardChoices
## X-squared = 29.237, df = 9, p-value = 0.0005909# testing if the row totals (the frequencies for choice_1) are different from the column totals (the frequencies for choice_2)
mcnemar.test(cardChoices)##
## McNemar's Chi-squared test
##
## data: cardChoices
## McNemar's chi-squared = 16.033, df = 6, p-value = 0.013585.4 Comparing two means
5.4.1 The one-sample z-test
# Load data
load("~/lsr/lsr/analysis/input/zeppo.Rdata")
grades## [1] 50 60 60 64 66 66 67 69 70 74 76 76 77 79 79 79 81 82 82 89# Calculating z-test
# 1. sample mean
sample.mean <- mean(grades)
# 2. value of the population mean null hypothesis specifies
mu.null <- 67.5
# 3. assumed population standard deviation
sd.true <- 9.5
# 4. sample size
N <- length(grades)
# 5. calculate the true standard error of the mean
sem.true <- sd.true / sqrt(N)
# 6. calculate z-score
z.score <- (sample.mean - mu.null) / sem.true
z.score## [1] 2.259606# 7. calculate critical regions (area under the curve)
# upper tail
upper.area <- pnorm(q = z.score, lower.tail = F)
upper.area## [1] 0.01192287# lower tail
lower.area <- pnorm(q = -z.score, lower.tail = T)
lower.area## [1] 0.01192287# 8. calculate p-value
p.value <- lower.area + upper.area
p.value## [1] 0.023845745.4.2 The one-sample t-test
# running one-sample t-test (two sided test)
oneSampleTTest(x = grades, mu = 67.5)##
## One sample t-test
##
## Data variable: grades
##
## Descriptive statistics:
## grades
## mean 72.300
## std dev. 9.521
##
## Hypotheses:
## null: population mean equals 67.5
## alternative: population mean not equal to 67.5
##
## Test results:
## t-statistic: 2.255
## degrees of freedom: 19
## p-value: 0.036
##
## Other information:
## two-sided 95% confidence interval: [67.844, 76.756]
## estimated effect size (Cohen's d): 0.504# one sided test
oneSampleTTest(x = grades, mu = 67.5, one.sided = "greater")##
## One sample t-test
##
## Data variable: grades
##
## Descriptive statistics:
## grades
## mean 72.300
## std dev. 9.521
##
## Hypotheses:
## null: population mean less than or equal to 67.5
## alternative: population mean greater than 67.5
##
## Test results:
## t-statistic: 2.255
## degrees of freedom: 19
## p-value: 0.018
##
## Other information:
## one-sided 95% confidence interval: [68.619, Inf]
## estimated effect size (Cohen's d): 0.504# or
oneSampleTTest(x = grades, mu = 67.5, one.sided = "less")##
## One sample t-test
##
## Data variable: grades
##
## Descriptive statistics:
## grades
## mean 72.300
## std dev. 9.521
##
## Hypotheses:
## null: population mean greater than or equal to 67.5
## alternative: population mean less than 67.5
##
## Test results:
## t-statistic: 2.255
## degrees of freedom: 19
## p-value: 0.982
##
## Other information:
## one-sided 95% confidence interval: [-Inf, 75.981]
## estimated effect size (Cohen's d): 0.504# using t-test function
t.test(x = grades, mu = 67.5)##
## One Sample t-test
##
## data: grades
## t = 2.2547, df = 19, p-value = 0.03615
## alternative hypothesis: true mean is not equal to 67.5
## 95 percent confidence interval:
## 67.84422 76.75578
## sample estimates:
## mean of x
## 72.35.4.3 The independent samples t-test
# Load the data
load("~/lsr/lsr/analysis/input/harpo.Rdata")
harpo| grade | tutor |
|---|---|
| 65 | Anastasia |
| 72 | Bernadette |
| 66 | Bernadette |
| 74 | Anastasia |
| 73 | Anastasia |
| 71 | Bernadette |
| 66 | Bernadette |
| 76 | Bernadette |
| 69 | Bernadette |
| 79 | Bernadette |
| 73 | Bernadette |
| 62 | Bernadette |
| 83 | Anastasia |
| 76 | Anastasia |
| 69 | Bernadette |
| 68 | Bernadette |
| 65 | Anastasia |
| 86 | Anastasia |
| 60 | Bernadette |
| 70 | Anastasia |
| 80 | Anastasia |
| 73 | Bernadette |
| 68 | Bernadette |
| 55 | Anastasia |
| 67 | Bernadette |
| 78 | Anastasia |
| 78 | Anastasia |
| 90 | Anastasia |
| 77 | Anastasia |
| 74 | Bernadette |
| 56 | Bernadette |
| 68 | Anastasia |
| 74 | Bernadette |
# Parameters for plots
emphCol <- rgb(0, 0, 1)
emphColLight <- rgb(.5, .5, 1)
emphGrey <- grey(.5)
colour <- TRUE
# Plotting histograms
harpoHist <- function() {
plotHist <- function(x, ...) {
hist(x,
border = "white",
col = ifelse(colour, emphColLight, emphGrey), ...
)
axis(1)
}
# Anastasia
plotHist(harpo$grade[harpo$tutor == "Anastasia"],
xlim = c(50, 100), xlab = "Grade", main = "Anastasia's students",
font.main = 1, breaks = seq(50, 100, 5), ylim = c(0, 7)
)
# Bernadette
plotHist(harpo$grade[harpo$tutor == "Bernadette"],
xlim = c(50, 100), xlab = "Grade", main = "Bernadette's students",
font.main = 1, breaks = seq(50, 100, 5), ylim = c(0, 7)
)
}
harpoHist()
# Plotting means and CIs
harpoMeans <- function() {
plotmeans(
formula = grade ~ tutor, # plot grade by test time
data = harpo, # data frame
n.label = FALSE, # don't show sample size
xlab = "Class", # x-axis label
ylab = "Grade" # y-axis label
)
# now add the line...
abline(
a = 0, # line has an intercept at 0
b = 1 # and a slope of 1
)
}
harpoMeans()
# running the Student's independent samples t-test (two sided test)
independentSamplesTTest(formula = grade ~ tutor, data = harpo, var.equal = T)##
## Student's independent samples t-test
##
## Outcome variable: grade
## Grouping variable: tutor
##
## Descriptive statistics:
## Anastasia Bernadette
## mean 74.533 69.056
## std dev. 8.999 5.775
##
## Hypotheses:
## null: population means equal for both groups
## alternative: different population means in each group
##
## Test results:
## t-statistic: 2.115
## degrees of freedom: 31
## p-value: 0.043
##
## Other information:
## two-sided 95% confidence interval: [0.197, 10.759]
## estimated effect size (Cohen's d): 0.74# running the Welch's independent samples t-test (two sided test)
independentSamplesTTest(formula = grade ~ tutor, data = harpo) # not equal variances assumed##
## Welch's independent samples t-test
##
## Outcome variable: grade
## Grouping variable: tutor
##
## Descriptive statistics:
## Anastasia Bernadette
## mean 74.533 69.056
## std dev. 8.999 5.775
##
## Hypotheses:
## null: population means equal for both groups
## alternative: different population means in each group
##
## Test results:
## t-statistic: 2.034
## degrees of freedom: 23.025
## p-value: 0.054
##
## Other information:
## two-sided 95% confidence interval: [-0.092, 11.048]
## estimated effect size (Cohen's d): 0.724# using t.test function (Welch's test)
t.test(formula = grade ~ tutor, data = harpo)##
## Welch Two Sample t-test
##
## data: grade by tutor
## t = 2.0342, df = 23.025, p-value = 0.05361
## alternative hypothesis: true difference in means between group Anastasia and group Bernadette is not equal to 0
## 95 percent confidence interval:
## -0.09249349 11.04804904
## sample estimates:
## mean in group Anastasia mean in group Bernadette
## 74.53333 69.05556# Student's test
t.test(formula = grade ~ tutor, data = harpo, var.equal = T)##
## Two Sample t-test
##
## data: grade by tutor
## t = 2.1154, df = 31, p-value = 0.04253
## alternative hypothesis: true difference in means between group Anastasia and group Bernadette is not equal to 0
## 95 percent confidence interval:
## 0.1965873 10.7589683
## sample estimates:
## mean in group Anastasia mean in group Bernadette
## 74.53333 69.05556# one sided test
independentSamplesTTest(formula = grade ~ tutor, data = harpo, one.sided = "Anastasia")##
## Welch's independent samples t-test
##
## Outcome variable: grade
## Grouping variable: tutor
##
## Descriptive statistics:
## Anastasia Bernadette
## mean 74.533 69.056
## std dev. 8.999 5.775
##
## Hypotheses:
## null: population means are equal, or smaller for group 'Anastasia'
## alternative: population mean is larger for group 'Anastasia'
##
## Test results:
## t-statistic: 2.034
## degrees of freedom: 23.025
## p-value: 0.027
##
## Other information:
## one-sided 95% confidence interval: [0.863, Inf]
## estimated effect size (Cohen's d): 0.724# or
independentSamplesTTest(formula = grade ~ tutor, data = harpo, one.sided = "Bernadette")##
## Welch's independent samples t-test
##
## Outcome variable: grade
## Grouping variable: tutor
##
## Descriptive statistics:
## Anastasia Bernadette
## mean 74.533 69.056
## std dev. 8.999 5.775
##
## Hypotheses:
## null: population means are equal, or smaller for group 'Bernadette'
## alternative: population mean is larger for group 'Bernadette'
##
## Test results:
## t-statistic: 2.034
## degrees of freedom: 23.025
## p-value: 0.973
##
## Other information:
## one-sided 95% confidence interval: [-Inf, 10.093]
## estimated effect size (Cohen's d): 0.7245.4.4 The paired-samples t-test
# load data
load("~/lsr/lsr/analysis/input/chico.Rdata")
chico| id | grade_test1 | grade_test2 |
|---|---|---|
| student1 | 42.9 | 44.6 |
| student2 | 51.8 | 54.0 |
| student3 | 71.7 | 72.3 |
| student4 | 51.6 | 53.4 |
| student5 | 63.5 | 63.8 |
| student6 | 58.0 | 59.3 |
| student7 | 59.8 | 60.8 |
| student8 | 50.8 | 51.6 |
| student9 | 62.5 | 64.3 |
| student10 | 61.9 | 63.2 |
| student11 | 50.4 | 51.8 |
| student12 | 52.6 | 52.2 |
| student13 | 63.0 | 63.0 |
| student14 | 58.3 | 60.5 |
| student15 | 53.3 | 57.1 |
| student16 | 58.7 | 60.1 |
| student17 | 50.1 | 51.7 |
| student18 | 64.2 | 65.6 |
| student19 | 57.4 | 58.3 |
| student20 | 57.1 | 60.1 |
describe(chico)| vars | n | mean | sd | median | trimmed | mad | min | max | range | skew | kurtosis | se | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| id* | 1 | 20 | 10.500 | 5.916080 | 10.5 | 10.50000 | 7.41300 | 1.0 | 20.0 | 19.0 | 0.0000000 | -1.3809286 | 1.322876 |
| grade_test1 | 2 | 20 | 56.980 | 6.616137 | 57.7 | 56.91875 | 7.70952 | 42.9 | 71.7 | 28.8 | 0.0540357 | -0.3549756 | 1.479413 |
| grade_test2 | 3 | 20 | 58.385 | 6.405612 | 59.7 | 58.35000 | 6.44931 | 44.6 | 72.3 | 27.7 | -0.0538576 | -0.3892926 | 1.432338 |
# create a "difference" variable
chico$improvement <- chico$grade_test2 - chico$grade_test1
chico| id | grade_test1 | grade_test2 | improvement |
|---|---|---|---|
| student1 | 42.9 | 44.6 | 1.7 |
| student2 | 51.8 | 54.0 | 2.2 |
| student3 | 71.7 | 72.3 | 0.6 |
| student4 | 51.6 | 53.4 | 1.8 |
| student5 | 63.5 | 63.8 | 0.3 |
| student6 | 58.0 | 59.3 | 1.3 |
| student7 | 59.8 | 60.8 | 1.0 |
| student8 | 50.8 | 51.6 | 0.8 |
| student9 | 62.5 | 64.3 | 1.8 |
| student10 | 61.9 | 63.2 | 1.3 |
| student11 | 50.4 | 51.8 | 1.4 |
| student12 | 52.6 | 52.2 | -0.4 |
| student13 | 63.0 | 63.0 | 0.0 |
| student14 | 58.3 | 60.5 | 2.2 |
| student15 | 53.3 | 57.1 | 3.8 |
| student16 | 58.7 | 60.1 | 1.4 |
| student17 | 50.1 | 51.7 | 1.6 |
| student18 | 64.2 | 65.6 | 1.4 |
| student19 | 57.4 | 58.3 | 0.9 |
| student20 | 57.1 | 60.1 | 3.0 |
# running a paired samples t-test
#
# Option 1:
# a. create a "difference" variable (chico$improvement)
# b. run a one sample t-test on it
oneSampleTTest(chico$improvement, mu = 0)##
## One sample t-test
##
## Data variable: chico$improvement
##
## Descriptive statistics:
## improvement
## mean 1.405
## std dev. 0.970
##
## Hypotheses:
## null: population mean equals 0
## alternative: population mean not equal to 0
##
## Test results:
## t-statistic: 6.475
## degrees of freedom: 19
## p-value: <.001
##
## Other information:
## two-sided 95% confidence interval: [0.951, 1.859]
## estimated effect size (Cohen's d): 1.448# Option 2:
# using the pairedSamplesTTest function from lsr package (one sided formula) (two sided test)
pairedSamplesTTest(formula = ~ grade_test2 + grade_test1, data = chico)##
## Paired samples t-test
##
## Variables: grade_test2 , grade_test1
##
## Descriptive statistics:
## grade_test2 grade_test1 difference
## mean 58.385 56.980 1.405
## std dev. 6.406 6.616 0.970
##
## Hypotheses:
## null: population means equal for both measurements
## alternative: different population means for each measurement
##
## Test results:
## t-statistic: 6.475
## degrees of freedom: 19
## p-value: <.001
##
## Other information:
## two-sided 95% confidence interval: [0.951, 1.859]
## estimated effect size (Cohen's d): 1.448#
# one sided test
pairedSamplesTTest(formula = ~ grade_test2 + grade_test1, data = chico, one.sided = "grade_test2")##
## Paired samples t-test
##
## Variables: grade_test2 , grade_test1
##
## Descriptive statistics:
## grade_test2 grade_test1 difference
## mean 58.385 56.980 1.405
## std dev. 6.406 6.616 0.970
##
## Hypotheses:
## null: population means are equal, or smaller for measurement 'grade_test2'
## alternative: population mean is larger for measurement 'grade_test2'
##
## Test results:
## t-statistic: 6.475
## degrees of freedom: 19
## p-value: <.001
##
## Other information:
## one-sided 95% confidence interval: [1.03, Inf]
## estimated effect size (Cohen's d): 1.448# running a paired samples t-test from long form data
# first, format df from wide to long
chico2 <- wideToLong(chico, within = "time")
chico2| id | improvement | time | grade |
|---|---|---|---|
| student1 | 1.7 | test1 | 42.9 |
| student2 | 2.2 | test1 | 51.8 |
| student3 | 0.6 | test1 | 71.7 |
| student4 | 1.8 | test1 | 51.6 |
| student5 | 0.3 | test1 | 63.5 |
| student6 | 1.3 | test1 | 58.0 |
| student7 | 1.0 | test1 | 59.8 |
| student8 | 0.8 | test1 | 50.8 |
| student9 | 1.8 | test1 | 62.5 |
| student10 | 1.3 | test1 | 61.9 |
| student11 | 1.4 | test1 | 50.4 |
| student12 | -0.4 | test1 | 52.6 |
| student13 | 0.0 | test1 | 63.0 |
| student14 | 2.2 | test1 | 58.3 |
| student15 | 3.8 | test1 | 53.3 |
| student16 | 1.4 | test1 | 58.7 |
| student17 | 1.6 | test1 | 50.1 |
| student18 | 1.4 | test1 | 64.2 |
| student19 | 0.9 | test1 | 57.4 |
| student20 | 3.0 | test1 | 57.1 |
| student1 | 1.7 | test2 | 44.6 |
| student2 | 2.2 | test2 | 54.0 |
| student3 | 0.6 | test2 | 72.3 |
| student4 | 1.8 | test2 | 53.4 |
| student5 | 0.3 | test2 | 63.8 |
| student6 | 1.3 | test2 | 59.3 |
| student7 | 1.0 | test2 | 60.8 |
| student8 | 0.8 | test2 | 51.6 |
| student9 | 1.8 | test2 | 64.3 |
| student10 | 1.3 | test2 | 63.2 |
| student11 | 1.4 | test2 | 51.8 |
| student12 | -0.4 | test2 | 52.2 |
| student13 | 0.0 | test2 | 63.0 |
| student14 | 2.2 | test2 | 60.5 |
| student15 | 3.8 | test2 | 57.1 |
| student16 | 1.4 | test2 | 60.1 |
| student17 | 1.6 | test2 | 51.7 |
| student18 | 1.4 | test2 | 65.6 |
| student19 | 0.9 | test2 | 58.3 |
| student20 | 3.0 | test2 | 60.1 |
# second, using the pairedSamplesTTest (two sided formula)
# Option 1 (two sided test)
pairedSamplesTTest(formula = grade ~ time, data = chico2, id = "id")##
## Paired samples t-test
##
## Outcome variable: grade
## Grouping variable: time
## ID variable: id
##
## Descriptive statistics:
## test1 test2 difference
## mean 56.980 58.385 -1.405
## std dev. 6.616 6.406 0.970
##
## Hypotheses:
## null: population means equal for both measurements
## alternative: different population means for each measurement
##
## Test results:
## t-statistic: -6.475
## degrees of freedom: 19
## p-value: <.001
##
## Other information:
## two-sided 95% confidence interval: [-1.859, -0.951]
## estimated effect size (Cohen's d): 1.448# one sided test
pairedSamplesTTest(formula = grade ~ time, data = chico2, id = "id", one.sided = "test2")##
## Paired samples t-test
##
## Outcome variable: grade
## Grouping variable: time
## ID variable: id
##
## Descriptive statistics:
## test1 test2 difference
## mean 56.980 58.385 -1.405
## std dev. 6.616 6.406 0.970
##
## Hypotheses:
## null: population means are equal, or smaller for measurement 'test2'
## alternative: population mean is larger for measurement 'test2'
##
## Test results:
## t-statistic: -6.475
## degrees of freedom: 19
## p-value: <.001
##
## Other information:
## one-sided 95% confidence interval: [-Inf, -1.03]
## estimated effect size (Cohen's d): 1.448# Option 2
pairedSamplesTTest(formula = grade ~ time + (id), data = chico2)##
## Paired samples t-test
##
## Outcome variable: grade
## Grouping variable: time
## ID variable: id
##
## Descriptive statistics:
## test1 test2 difference
## mean 56.980 58.385 -1.405
## std dev. 6.616 6.406 0.970
##
## Hypotheses:
## null: population means equal for both measurements
## alternative: different population means for each measurement
##
## Test results:
## t-statistic: -6.475
## degrees of freedom: 19
## p-value: <.001
##
## Other information:
## two-sided 95% confidence interval: [-1.859, -0.951]
## estimated effect size (Cohen's d): 1.448# using t.test function
t.test(x = chico$grade_test2, y = chico$grade_test1, paired = T) # the first element of x and y must correspond to the same person##
## Paired t-test
##
## data: chico$grade_test2 and chico$grade_test1
## t = 6.4754, df = 19, p-value = 0.000003321
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
## 0.9508686 1.8591314
## sample estimates:
## mean of the differences
## 1.405# one sided test
pairedSamplesTTest(formula = grade ~ time + (id), data = chico2, one.sided = "test2")##
## Paired samples t-test
##
## Outcome variable: grade
## Grouping variable: time
## ID variable: id
##
## Descriptive statistics:
## test1 test2 difference
## mean 56.980 58.385 -1.405
## std dev. 6.616 6.406 0.970
##
## Hypotheses:
## null: population means are equal, or smaller for measurement 'test2'
## alternative: population mean is larger for measurement 'test2'
##
## Test results:
## t-statistic: -6.475
## degrees of freedom: 19
## p-value: <.001
##
## Other information:
## one-sided 95% confidence interval: [-Inf, -1.03]
## estimated effect size (Cohen's d): 1.4485.4.5 Effect size
# Cohen's d from one sample
cohensD(x = grades, mu = 67.5)## [1] 0.5041691# Cohen's d from a Student t-test
cohensD(formula = grade ~ tutor, data = harpo, method = "pooled")## [1] 0.7395614# Cohen's d from a Welch t-test
cohensD(formula = grade ~ tutor, data = harpo, method = "unequal")## [1] 0.72449955.4.6 Checking the normality of a sample
# generating data
normal.data <- rnorm(n = 100)
# plotting data
hist(x = normal.data)
qqnorm(y = normal.data)
# running a Whapiro-Wilk test
shapiro.test(x = normal.data)##
## Shapiro-Wilk normality test
##
## data: normal.data
## W = 0.99108, p-value = 0.75165.4.7 Testing non-normal data with Wilcoxon tests
# load data
load("~/lsr/lsr/analysis/input/awesome.Rdata")
load("~/lsr/lsr/analysis/input/awesome2.Rdata")
load("~/lsr/lsr/analysis/input/happy.Rdata")
awesome| scores | group |
|---|---|
| 6.4 | A |
| 10.7 | A |
| 11.9 | A |
| 7.3 | A |
| 10.0 | A |
| 14.5 | B |
| 10.4 | B |
| 12.9 | B |
| 11.7 | B |
| 13.0 | B |
score.A## [1] 6.4 10.7 11.9 7.3 10.0score.B## [1] 14.5 10.4 12.9 11.7 13.0happiness| before | after | change |
|---|---|---|
| 30 | 6 | -24 |
| 43 | 29 | -14 |
| 21 | 11 | -10 |
| 24 | 31 | 7 |
| 23 | 17 | -6 |
| 40 | 2 | -38 |
| 29 | 31 | 2 |
| 56 | 21 | -35 |
| 38 | 8 | -30 |
| 16 | 21 | 5 |
# running the two sample Wilcoxon test
wilcox.test(formula = scores ~ group, data = awesome)##
## Wilcoxon rank sum exact test
##
## data: scores by group
## W = 3, p-value = 0.05556
## alternative hypothesis: true location shift is not equal to 0# for data stored separately for each group
wilcox.test(x = score.A, y = score.B)##
## Wilcoxon rank sum exact test
##
## data: score.A and score.B
## W = 3, p-value = 0.05556
## alternative hypothesis: true location shift is not equal to 0# running the one sample Wilcoxon test
wilcox.test(x = happiness$change, mu = 0)##
## Wilcoxon signed rank exact test
##
## data: happiness$change
## V = 7, p-value = 0.03711
## alternative hypothesis: true location is not equal to 0# or
wilcox.test(x = happiness$after, y = happiness$before, paired = T)##
## Wilcoxon signed rank exact test
##
## data: happiness$after and happiness$before
## V = 7, p-value = 0.03711
## alternative hypothesis: true location shift is not equal to 05.5 Comparing several means (one-way ANOVA)
# load data
load("~/lsr/lsr/analysis/input/clinicaltrial.Rdata")
clin.trial| drug | therapy | mood.gain |
|---|---|---|
| placebo | no.therapy | 0.5 |
| placebo | no.therapy | 0.3 |
| placebo | no.therapy | 0.1 |
| anxifree | no.therapy | 0.6 |
| anxifree | no.therapy | 0.4 |
| anxifree | no.therapy | 0.2 |
| joyzepam | no.therapy | 1.4 |
| joyzepam | no.therapy | 1.7 |
| joyzepam | no.therapy | 1.3 |
| placebo | CBT | 0.6 |
| placebo | CBT | 0.9 |
| placebo | CBT | 0.3 |
| anxifree | CBT | 1.1 |
| anxifree | CBT | 0.8 |
| anxifree | CBT | 1.2 |
| joyzepam | CBT | 1.8 |
| joyzepam | CBT | 1.3 |
| joyzepam | CBT | 1.4 |
# descriptive statistics
# how many people in each group
xtabs(~drug, clin.trial)## drug
## placebo anxifree joyzepam
## 6 6 6# calculating means and sd
mood.gain.mean <- aggregate(mood.gain ~ drug, clin.trial, mean) |>
rename(mood.gain.mean = mood.gain)
mood.gain.sd <- aggregate(mood.gain ~ drug, clin.trial, sd) |>
rename(mood.gain.sd = mood.gain)
mood.gain.mean| drug | mood.gain.mean |
|---|---|
| placebo | 0.4500000 |
| anxifree | 0.7166667 |
| joyzepam | 1.4833333 |
mood.gain.sd| drug | mood.gain.sd |
|---|---|
| placebo | 0.2810694 |
| anxifree | 0.3920034 |
| joyzepam | 0.2136976 |
# plotting the results
plotmeans(
formula = mood.gain ~ drug,
data = clin.trial,
xlab = "Drug Administered",
ylab = "Mood Gain",
n.label = F
)
# calculating the within-group sum of squares
outcome <- clin.trial$mood.gain
group <- clin.trial$drug
gp.means <- tapply(outcome, group, mean)
gp.means <- gp.means[group]
dev.from.gp.means <- outcome - gp.means
squared.devs <- dev.from.gp.means^2
Y <- data.frame(group, outcome, gp.means, dev.from.gp.means, squared.devs)
Y| group | outcome | gp.means | dev.from.gp.means | squared.devs |
|---|---|---|---|---|
| placebo | 0.5 | 0.4500000 | 0.0500000 | 0.0025000 |
| placebo | 0.3 | 0.4500000 | -0.1500000 | 0.0225000 |
| placebo | 0.1 | 0.4500000 | -0.3500000 | 0.1225000 |
| anxifree | 0.6 | 0.7166667 | -0.1166667 | 0.0136111 |
| anxifree | 0.4 | 0.7166667 | -0.3166667 | 0.1002778 |
| anxifree | 0.2 | 0.7166667 | -0.5166667 | 0.2669444 |
| joyzepam | 1.4 | 1.4833333 | -0.0833333 | 0.0069444 |
| joyzepam | 1.7 | 1.4833333 | 0.2166667 | 0.0469444 |
| joyzepam | 1.3 | 1.4833333 | -0.1833333 | 0.0336111 |
| placebo | 0.6 | 0.4500000 | 0.1500000 | 0.0225000 |
| placebo | 0.9 | 0.4500000 | 0.4500000 | 0.2025000 |
| placebo | 0.3 | 0.4500000 | -0.1500000 | 0.0225000 |
| anxifree | 1.1 | 0.7166667 | 0.3833333 | 0.1469444 |
| anxifree | 0.8 | 0.7166667 | 0.0833333 | 0.0069444 |
| anxifree | 1.2 | 0.7166667 | 0.4833333 | 0.2336111 |
| joyzepam | 1.8 | 1.4833333 | 0.3166667 | 0.1002778 |
| joyzepam | 1.3 | 1.4833333 | -0.1833333 | 0.0336111 |
| joyzepam | 1.4 | 1.4833333 | -0.0833333 | 0.0069444 |
SSw <- sum(squared.devs)
SSw## [1] 1.391667# calculating the between-group sum of squares
gp.means <- tapply(outcome, group, mean)
grand.mean <- mean(outcome)
dev.from.grand.mean <- gp.means - grand.mean
squared.devs <- dev.from.grand.mean^2
gp.sizes <- tapply(outcome, group, length)
wt.squared.devs <- gp.sizes * squared.devs
Y <- data.frame(gp.means, grand.mean, dev.from.grand.mean, squared.devs, gp.sizes, wt.squared.devs)
Y| gp.means | grand.mean | dev.from.grand.mean | squared.devs | gp.sizes | wt.squared.devs | |
|---|---|---|---|---|---|---|
| placebo | 0.4500000 | 0.8833333 | -0.4333333 | 0.1877778 | 6 | 1.1266667 |
| anxifree | 0.7166667 | 0.8833333 | -0.1666667 | 0.0277778 | 6 | 0.1666667 |
| joyzepam | 1.4833333 | 0.8833333 | 0.6000000 | 0.3600000 | 6 | 2.1600000 |
SSb <- sum(wt.squared.devs)
SSb## [1] 3.453333# calculating df (G = 3, N = 18)
df_b <- 3 - 1
df_w <- 18 - 3
# calculating the mean square values
MS_b <- 3.45 / df_b
MS_w <- 1.39 / df_w
# calculating F-value
F <- MS_b / MS_w
F## [1] 18.61511# calculating p-value
pf(F, df1 = 2, df2 = 15, lower.tail = F)## [1] 0.9999136# calculating ANOVA with aov()
my.anova <- aov(mood.gain ~ drug, clin.trial)
my.anova## Call:
## aov(formula = mood.gain ~ drug, data = clin.trial)
##
## Terms:
## drug Residuals
## Sum of Squares 3.453333 1.391667
## Deg. of Freedom 2 15
##
## Residual standard error: 0.3045944
## Estimated effects may be unbalancedsummary(my.anova)## Df Sum Sq Mean Sq F value Pr(>F)
## drug 2 3.453 1.7267 18.61 0.0000865 ***
## Residuals 15 1.392 0.0928
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1# calculating the effect size (eta squared)
SStot <- SSb + SSw
eta.squared <- SSb / SStot
eta.squared## [1] 0.7127623# or
etaSquared(x = my.anova)## eta.sq eta.sq.part
## drug 0.7127623 0.71276235.5.1 Multiple comparisons and post hoc tests
# the tidy way
placebo <- clin.trial |>
filter(drug == "placebo") |>
select(mood.gain)
placebo <- placebo[, 1]
anxifree <- clin.trial |>
filter(drug == "anxifree") |>
select(mood.gain)
anxifree <- anxifree[, 1]
joyzepam <- clin.trial |>
filter(drug == "joyzepam") |>
select(mood.gain)
joyzepam <- joyzepam[, 1]
# the non-tidy way
joyzepam <- with(clin.trial, mood.gain[drug == "joyzepam"]) # mood change due to joyzepam
anxifree <- with(clin.trial, mood.gain[drug == "anxifree"]) # mood change due to anxifree
placebo <- with(clin.trial, mood.gain[drug == "placebo"]) # mood change due to placebo
# running "pairwise" t-tests
t.test(anxifree, placebo, var.equal = TRUE) # Student t-test##
## Two Sample t-test
##
## data: anxifree and placebo
## t = 1.3542, df = 10, p-value = 0.2055
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
## -0.1721001 0.7054334
## sample estimates:
## mean of x mean of y
## 0.7166667 0.4500000# or
t.test(
formula = mood.gain ~ drug,
data = clin.trial,
subset = drug %in% c("placebo", "anxifree"),
var.equal = TRUE
)##
## Two Sample t-test
##
## data: mood.gain by drug
## t = -1.3542, df = 10, p-value = 0.2055
## alternative hypothesis: true difference in means between group placebo and group anxifree is not equal to 0
## 95 percent confidence interval:
## -0.7054334 0.1721001
## sample estimates:
## mean in group placebo mean in group anxifree
## 0.4500000 0.7166667# or
pairwise.t.test(
x = clin.trial$mood.gain, # outcome variable
g = clin.trial$drug, # grouping variable
p.adjust.method = "none" # which correction to use
)##
## Pairwise comparisons using t tests with pooled SD
##
## data: clin.trial$mood.gain and clin.trial$drug
##
## placebo anxifree
## anxifree 0.15021 -
## joyzepam 0.00003 0.00056
##
## P value adjustment method: none# or
posthocPairwiseT(x = my.anova, p.adjust.method = "none") # calling pairwise.t.test using an aov object##
## Pairwise comparisons using t tests with pooled SD
##
## data: mood.gain and drug
##
## placebo anxifree
## anxifree 0.15021 -
## joyzepam 0.00003 0.00056
##
## P value adjustment method: none# corrections for multiple testing
# Bonferroni corrections
posthocPairwiseT(my.anova, p.adjust.method = "bonferroni")##
## Pairwise comparisons using t tests with pooled SD
##
## data: mood.gain and drug
##
## placebo anxifree
## anxifree 0.4506 -
## joyzepam 0.000091 0.0017
##
## P value adjustment method: bonferroni# Holm correction
posthocPairwiseT(my.anova)##
## Pairwise comparisons using t tests with pooled SD
##
## data: mood.gain and drug
##
## placebo anxifree
## anxifree 0.1502 -
## joyzepam 0.000091 0.0011
##
## P value adjustment method: holm5.5.2 Checking the homogeneity of variance assumption
# running the Levene's test
leveneTest(y = my.anova, center = mean) # mean| Df | F value | Pr(>F) | |
|---|---|---|---|
| group | 2 | 1.449739 | 0.2656941 |
| 15 | NA | NA |
# or
leveneTest(y = mood.gain ~ drug, data = clin.trial) # y is a formula in this case| Df | F value | Pr(>F) | |
|---|---|---|---|
| group | 2 | 1.467181 | 0.2618423 |
| 15 | NA | NA |
# or
leveneTest(y = clin.trial$mood.gain, group = clin.trial$drug) # y is the outcome| Df | F value | Pr(>F) | |
|---|---|---|---|
| group | 2 | 1.467181 | 0.2618423 |
| 15 | NA | NA |
# running the Brown-Forsythe test (default)
leveneTest(my.anova) # median| Df | F value | Pr(>F) | |
|---|---|---|---|
| group | 2 | 1.467181 | 0.2618423 |
| 15 | NA | NA |
5.5.3 Removing the homogeneity of variance assumption
# running the Welch one-way test
oneway.test(mood.gain ~ drug, data = clin.trial)##
## One-way analysis of means (not assuming equal variances)
##
## data: mood.gain and drug
## F = 26.322, num df = 2.0000, denom df = 9.4932, p-value = 0.0001345.5.4 Checking the normality assumption
# extract the residuals
my.anova.residuals <- residuals(object = my.anova)
my.anova.residuals## 1 2 3 4 5 6
## 0.05000000 -0.15000000 -0.35000000 -0.11666667 -0.31666667 -0.51666667
## 7 8 9 10 11 12
## -0.08333333 0.21666667 -0.18333333 0.15000000 0.45000000 -0.15000000
## 13 14 15 16 17 18
## 0.38333333 0.08333333 0.48333333 0.31666667 -0.18333333 -0.08333333# plotting the results to check normality
hist(x = my.anova.residuals)
qqnorm(y = my.anova.residuals)
shapiro.test(x = my.anova.residuals)##
## Shapiro-Wilk normality test
##
## data: my.anova.residuals
## W = 0.96019, p-value = 0.60535.5.5 Removing the normality assumption
# running the Kruskal-Wallis test
kruskal.test(mood.gain ~ drug, data = clin.trial)##
## Kruskal-Wallis rank sum test
##
## data: mood.gain by drug
## Kruskal-Wallis chi-squared = 12.076, df = 2, p-value = 0.002386# or
kruskal.test(x = clin.trial$mood.gain, g = clin.trial$drug)##
## Kruskal-Wallis rank sum test
##
## data: clin.trial$mood.gain and clin.trial$drug
## Kruskal-Wallis chi-squared = 12.076, df = 2, p-value = 0.002386# or
mood.gain <- list(placebo, joyzepam, anxifree)
kruskal.test(x = mood.gain)##
## Kruskal-Wallis rank sum test
##
## data: mood.gain
## Kruskal-Wallis chi-squared = 12.076, df = 2, p-value = 0.0023865.6 Linear regression
# parameter to function drawBasicScatterplot
emphGrey <- grey(.5)
# plotting scatterplots (directly)
# plot(x = parenthood$dan.sleep, y = parenthood$dan.grump,
# xlab = "Dan Sleep (hours)",
# ylab = "Dan Grumpiness (0-100)")
# plot(x = parenthood$baby.sleep, y = parenthood$dan.grump)
# function to plot scatterplots
drawBasicScatterplot <- function(dotcol, title) {
plot(parenthood$dan.sleep,
parenthood$dan.grump,
xlab = "Dan Sleep (hours)",
ylab = "Dan Grumpiness (0-100)",
col = dotcol,
main = title,
font.main = 1,
pch = 19
)
}
drawBasicScatterplot(emphGrey, "")
# potting a depiction of the residuals associated with the best fitting regression line
# good regression line
drawBasicScatterplot(emphGrey, "Regression Line Close to the Data")
good.coef <- lm(dan.grump ~ dan.sleep, parenthood)$coef
abline(good.coef, col = ifelse(colour, emphCol, "black"), lwd = 3)
for (i in seq_along(parenthood$dan.sleep)) {
xval <- parenthood$dan.sleep[i] * c(1, 1)
yval <- c(parenthood$dan.grump[i], good.coef[1] + good.coef[2] * parenthood$dan.sleep[i])
lines(xval, yval, type = "l", col = emphGrey)
}
# bad regression line
drawBasicScatterplot(emphGrey, "Regression Line Distant from the Data")
bad.coef <- c(80, -3)
abline(bad.coef, col = ifelse(colour, emphCol, "black"), lwd = 3)
for (i in seq_along(parenthood$dan.sleep)) {
xval <- parenthood$dan.sleep[i] * c(1, 1)
yval <- c(parenthood$dan.grump[i], bad.coef[1] + bad.coef[2] * parenthood$dan.sleep[i])
lines(xval, yval, type = "l", col = emphGrey)
}
# running a simple regression model
regression.1 <- lm(dan.grump ~ dan.sleep, data = parenthood)
regression.1##
## Call:
## lm(formula = dan.grump ~ dan.sleep, data = parenthood)
##
## Coefficients:
## (Intercept) dan.sleep
## 125.956 -8.937# running a multiple linear regression
regression.2 <- lm(dan.grump ~ dan.sleep + baby.sleep, data = parenthood)
regression.2##
## Call:
## lm(formula = dan.grump ~ dan.sleep + baby.sleep, data = parenthood)
##
## Coefficients:
## (Intercept) dan.sleep baby.sleep
## 125.96557 -8.95025 0.010525.6.1 Quantifying the fit of the regression model
# The R-squared value
X <- parenthood$dan.sleep # the predictor
Y <- parenthood$dan.grump # the outcome
Y.pred <- -8.94 * X + 125.97
# calculating the sum of squared residuals
SS.resid <- sum((Y - Y.pred)^2)
SS.resid## [1] 1838.722# calculating the total sum of squares
SS.tot <- sum((Y - mean(Y))^2)
SS.tot## [1] 9998.59# calculating the coefficient of determination or R-squared
R.squared <- 1 - (SS.resid / SS.tot)
R.squared## [1] 0.8161018# relation between regression and correlation
# calculation correlation (r-Pearson correlation coefficient)
r <- cor(X, Y)
r^2## [1] 0.81610275.6.2 Hypothesis test for regression models
# compute all the quantities of the regression model
summary(regression.2)##
## Call:
## lm(formula = dan.grump ~ dan.sleep + baby.sleep, data = parenthood)
##
## Residuals:
## Min 1Q Median 3Q Max
## -11.0345 -2.2198 -0.4016 2.6775 11.7496
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 125.96557 3.04095 41.423 <0.0000000000000002 ***
## dan.sleep -8.95025 0.55346 -16.172 <0.0000000000000002 ***
## baby.sleep 0.01052 0.27106 0.039 0.969
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 4.354 on 97 degrees of freedom
## Multiple R-squared: 0.8161, Adjusted R-squared: 0.8123
## F-statistic: 215.2 on 2 and 97 DF, p-value: < 0.000000000000000225.6.3 Hypothesis test for a single correlation
# running t-test on a coefficient in a regression model
summary(regression.1)##
## Call:
## lm(formula = dan.grump ~ dan.sleep, data = parenthood)
##
## Residuals:
## Min 1Q Median 3Q Max
## -11.025 -2.213 -0.399 2.681 11.750
##
## Coefficients:
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 125.9563 3.0161 41.76 <0.0000000000000002 ***
## dan.sleep -8.9368 0.4285 -20.85 <0.0000000000000002 ***
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
##
## Residual standard error: 4.332 on 98 degrees of freedom
## Multiple R-squared: 0.8161, Adjusted R-squared: 0.8142
## F-statistic: 434.9 on 1 and 98 DF, p-value: < 0.00000000000000022# is the same
cor.test(x = parenthood$dan.sleep, y = parenthood$dan.grump)##
## Pearson's product-moment correlation
##
## data: parenthood$dan.sleep and parenthood$dan.grump
## t = -20.854, df = 98, p-value < 0.00000000000000022
## alternative hypothesis: true correlation is not equal to 0
## 95 percent confidence interval:
## -0.9340614 -0.8594714
## sample estimates:
## cor
## -0.9033845.6.4 Regarding regression coefficients
# confidence intervals for the coefficients
confint(object = regression.2, level = .99)## 0.5 % 99.5 %
## (Intercept) 117.9755724 133.9555593
## dan.sleep -10.4044419 -7.4960575
## baby.sleep -0.7016868 0.7227357# calculating standardised regression coefficients
standardCoefs(regression.2)## b beta
## dan.sleep -8.95024973 -0.90474809
## baby.sleep 0.01052447 0.002172235.6.5 Model checking
# Residuals
# getting ordinary residuals
residuals(object = regression.2)## 1 2 3 4 5 6
## -2.1403095 4.7081942 1.9553640 -2.0602806 0.7194888 -0.4066133
## 7 8 9 10 11 12
## 0.2269987 -1.7003077 0.2025039 3.8524589 3.9986291 -4.9120150
## 13 14 15 16 17 18
## 1.2060134 0.4946578 -2.6579276 -0.3966805 3.3538613 1.7261225
## 19 20 21 22 23 24
## -0.4922551 -5.6405941 -0.4660764 2.7238389 9.3653697 0.2841513
## 25 26 27 28 29 30
## -0.5037668 -1.4941146 8.1328623 1.9787316 -1.5126726 3.5171148
## 31 32 33 34 35 36
## -8.9256951 -2.8282946 6.1030349 -7.5460717 4.5572128 -10.6510836
## 37 38 39 40 41 42
## -5.6931846 6.3096506 -2.1082466 -0.5044253 0.1875576 4.8094841
## 43 44 45 46 47 48
## -5.4135163 -6.2292842 -4.5725232 -5.3354601 3.9950111 2.1718745
## 49 50 51 52 53 54
## -3.4766440 0.4834367 6.2839790 2.0109396 -1.5846631 -2.2166613
## 55 56 57 58 59 60
## 2.2033140 1.9328736 -1.8301204 -1.5401430 2.5298509 -3.3705782
## 61 62 63 64 65 66
## -2.9380806 0.6590736 -0.5917559 -8.6131971 5.9781035 5.9332979
## 67 68 69 70 71 72
## -1.2341956 3.0047669 -1.0802468 6.5174672 -3.0155469 2.1176720
## 73 74 75 76 77 78
## 0.6058757 -2.7237421 -2.2291472 -1.4053822 4.7461491 11.7495569
## 79 80 81 82 83 84
## 4.7634141 2.6620908 -11.0345292 -0.7588667 1.4558227 -0.4745727
## 85 86 87 88 89 90
## 8.9091201 -1.1409777 0.7555223 -0.4107130 0.8797237 -1.4095586
## 91 92 93 94 95 96
## 3.1571385 -3.4205757 -5.7228699 -2.2033958 -3.8647891 0.4982711
## 97 98 99 100
## -5.5249495 4.1134221 -8.2038533 5.6800859# getting standardised residuals
rstandard(model = regression.2)## 1 2 3 4 5 6
## -0.49675845 1.10430571 0.46361264 -0.47725357 0.16756281 -0.09488969
## 7 8 9 10 11 12
## 0.05286626 -0.39260381 0.04739691 0.89033990 0.95851248 -1.13898701
## 13 14 15 16 17 18
## 0.28047841 0.11519184 -0.61657092 -0.09191865 0.77692937 0.40403495
## 19 20 21 22 23 24
## -0.11552373 -1.31540412 -0.10819238 0.62951824 2.17129803 0.06586227
## 25 26 27 28 29 30
## -0.11980449 -0.34704024 1.91121833 0.45686516 -0.34986350 0.81233165
## 31 32 33 34 35 36
## -2.08659993 -0.66317843 1.42930082 -1.77763064 1.07452436 -2.47385780
## 37 38 39 40 41 42
## -1.32715114 1.49419658 -0.49115639 -0.11674947 0.04401233 1.11881912
## 43 44 45 46 47 48
## -1.27081641 -1.46422595 -1.06943700 -1.24659673 0.94152881 0.51069809
## 49 50 51 52 53 54
## -0.81373349 0.11412178 1.47938594 0.46437962 -0.37157009 -0.51609949
## 55 56 57 58 59 60
## 0.51800753 0.44813204 -0.42662358 -0.35575611 0.58403297 -0.78022677
## 61 62 63 64 65 66
## -0.67833325 0.15484699 -0.13760574 -2.05662232 1.40238029 1.37505125
## 67 68 69 70 71 72
## -0.28964989 0.69497632 -0.24945316 1.50709623 -0.69864682 0.49071427
## 73 74 75 76 77 78
## 0.14267297 -0.63246560 -0.51972828 -0.32509811 1.10842574 2.72171671
## 79 80 81 82 83 84
## 1.09975101 0.62057080 -2.55172097 -0.17584803 0.34340064 -0.11158952
## 85 86 87 88 89 90
## 2.10863391 -0.26386516 0.17624445 -0.09504416 0.20450884 -0.32730740
## 91 92 93 94 95 96
## 0.73475640 -0.79400855 -1.32768248 -0.51940736 -0.91512580 0.11661226
## 97 98 99 100
## -1.28069115 0.96332849 -1.90290258 1.31368144# getting Studentised residuals
rstudent(model = regression.2)## 1 2 3 4 5 6
## -0.49482102 1.10557030 0.46172854 -0.47534555 0.16672097 -0.09440368
## 7 8 9 10 11 12
## 0.05259381 -0.39088553 0.04715251 0.88938019 0.95810710 -1.14075472
## 13 14 15 16 17 18
## 0.27914212 0.11460437 -0.61459001 -0.09144760 0.77533036 0.40228555
## 19 20 21 22 23 24
## -0.11493461 -1.32043609 -0.10763974 0.62754813 2.21456485 0.06552336
## 25 26 27 28 29 30
## -0.11919416 -0.34546127 1.93818473 0.45499388 -0.34827522 0.81089646
## 31 32 33 34 35 36
## -2.12403286 -0.66125192 1.43712830 -1.79797263 1.07539064 -2.54258876
## 37 38 39 40 41 42
## -1.33244515 1.50388257 -0.48922682 -0.11615428 0.04378531 1.12028904
## 43 44 45 46 47 48
## -1.27490649 -1.47302872 -1.07023828 -1.25020935 0.94097261 0.50874322
## 49 50 51 52 53 54
## -0.81230544 0.11353962 1.48863006 0.46249410 -0.36991317 -0.51413868
## 55 56 57 58 59 60
## 0.51604474 0.44627831 -0.42481754 -0.35414868 0.58203894 -0.77864171
## 61 62 63 64 65 66
## -0.67643392 0.15406579 -0.13690795 -2.09211556 1.40949469 1.38147541
## 67 68 69 70 71 72
## -0.28827768 0.69311245 -0.24824363 1.51717578 -0.69679156 0.48878534
## 73 74 75 76 77 78
## 0.14195054 -0.63049841 -0.51776374 -0.32359434 1.10974786 2.81736616
## 79 80 81 82 83 84
## 1.10095270 0.61859288 -2.62827967 -0.17496714 0.34183379 -0.11101996
## 85 86 87 88 89 90
## 2.14753375 -0.26259576 0.17536170 -0.09455738 0.20349582 -0.32579584
## 91 92 93 94 95 96
## 0.73300184 -0.79248469 -1.33298848 -0.51744314 -0.91435205 0.11601774
## 97 98 99 100
## -1.28498273 0.96296745 -1.92942389 1.31867548# Anomalous data
# getting hat values
hatvalues(model = regression.2)## 1 2 3 4 5 6 7
## 0.02067452 0.04105320 0.06155445 0.01685226 0.02734865 0.03129943 0.02735579
## 8 9 10 11 12 13 14
## 0.01051224 0.03698976 0.01229155 0.08189763 0.01882551 0.02462902 0.02718388
## 15 16 17 18 19 20 21
## 0.01964210 0.01748592 0.01691392 0.03712530 0.04213891 0.02994643 0.02099435
## 22 23 24 25 26 27 28
## 0.01233280 0.01853370 0.01804801 0.06722392 0.02214927 0.04472007 0.01039447
## 29 30 31 32 33 34 35
## 0.01381812 0.01105817 0.03468260 0.04048248 0.03814670 0.04934440 0.05107803
## 36 37 38 39 40 41 42
## 0.02208177 0.02919013 0.05928178 0.02799695 0.01519967 0.04195751 0.02514137
## 43 44 45 46 47 48 49
## 0.04267879 0.04517340 0.03558080 0.03360160 0.05019778 0.04587468 0.03701290
## 50 51 52 53 54 55 56
## 0.05331282 0.04814477 0.01072699 0.04047386 0.02681315 0.04556787 0.01856997
## 57 58 59 60 61 62 63
## 0.02919045 0.01126069 0.01012683 0.01546412 0.01029534 0.04428870 0.02438944
## 64 65 66 67 68 69 70
## 0.07469673 0.04135090 0.01775697 0.04217616 0.01384321 0.01069005 0.01340216
## 71 72 73 74 75 76 77
## 0.01716361 0.01751844 0.04863314 0.02158623 0.02951418 0.01411915 0.03276064
## 78 79 80 81 82 83 84
## 0.01684599 0.01028001 0.02920514 0.01348051 0.01752758 0.05184527 0.04583604
## 85 86 87 88 89 90 91
## 0.05825858 0.01359644 0.03054414 0.01487724 0.02381348 0.02159418 0.02598661
## 92 93 94 95 96 97 98
## 0.02093288 0.01982480 0.05063492 0.05907629 0.03682026 0.01817919 0.03811718
## 99 100
## 0.01945603 0.01373394# getting Cook's distance values
cooks.distance(model = regression.2)## 1 2 3 4 5
## 0.00173651171 0.01740242936 0.00469937006 0.00130141703 0.00026315569
## 6 7 8 9 10
## 0.00009697585 0.00002620181 0.00054584906 0.00002876269 0.00328827681
## 11 12 13 14 15
## 0.02731835260 0.00829691897 0.00066214792 0.00012359557 0.00253891456
## 16 17 18 19 20
## 0.00005012283 0.00346174151 0.00209805468 0.00019570497 0.01780518526
## 21 22 23 24 25
## 0.00008367377 0.00164947783 0.02967593755 0.00002657610 0.00034480325
## 26 27 28 29 30
## 0.00090933792 0.05699951226 0.00073079434 0.00057169976 0.00245956350
## 31 32 33 34 35
## 0.05214331478 0.00618519973 0.02700686248 0.05467344690 0.02071643055
## 36 37 38 39 40
## 0.04606378152 0.01765311655 0.04689816875 0.00231612212 0.00007012530
## 41 42 43 44 45
## 0.00002827824 0.01076083119 0.02399930996 0.03381062226 0.01406497804
## 46 47 48 49 50
## 0.01801086321 0.01561698982 0.00417998637 0.00848351357 0.00024447866
## 51 52 53 54 55
## 0.03689945760 0.00077944724 0.00194123453 0.00244622954 0.00427036054
## 56 57 58 59 60
## 0.00126660900 0.00182421163 0.00048047048 0.00116318135 0.00318723481
## 61 62 63 64 65
## 0.00159551161 0.00037038258 0.00015778917 0.11381653127 0.02827715166
## 66 67 68 69 70
## 0.01139374043 0.00123142189 0.00226000648 0.00022413221 0.01028478940
## 71 72 73 74 75
## 0.00284132858 0.00143122276 0.00034685379 0.00294175691 0.00273824884
## 76 77 78 79 80
## 0.00050453567 0.01387108351 0.04230965547 0.00418744027 0.00386183094
## 81 82 83 84 85
## 0.02965826018 0.00018388884 0.00214936854 0.00019939290 0.09168733246
## 86 87 88 89 90
## 0.00031989944 0.00032621922 0.00004547383 0.00034008931 0.00078814872
## 91 92 93 94 95
## 0.00480120376 0.00449309454 0.01188426604 0.00479636047 0.01752665888
## 96 97 98 99 100
## 0.00017327933 0.01012301719 0.01225818302 0.02394963622 0.00801050779# test from car package to see if any of the Studentised residuals are significantly larger
outlierTest(model = regression.2)## No Studentized residuals with Bonferroni p < 0.05
## Largest |rstudent|:
## rstudent unadjusted p-value Bonferroni p
## 78 2.817366 0.0058788 0.58788# getting rid of outliers using subset
lm(formula = dan.grump ~ dan.sleep + baby.sleep, data = parenthood, subset = -64)##
## Call:
## lm(formula = dan.grump ~ dan.sleep + baby.sleep, data = parenthood,
## subset = -64)
##
## Coefficients:
## (Intercept) dan.sleep baby.sleep
## 126.3553 -8.8283 -0.1319# plotting anomalous data using plot()
plot(x = regression.2, which = 4) # Cook's distance 
plot(x = regression.2, which = 5) # the Studentised residuals agains leverage
# using the car package
influenceIndexPlot(model = regression.2)
influencePlot(model = regression.2)
| StudRes | Hat | CookD | |
|---|---|---|---|
| 11 | 0.9581071 | 0.0818976 | 0.0273184 |
| 64 | -2.0921156 | 0.0746967 | 0.1138165 |
| 78 | 2.8173662 | 0.0168460 | 0.0423097 |
| 81 | -2.6282797 | 0.0134805 | 0.0296583 |
| 85 | 2.1475338 | 0.0582586 | 0.0916873 |
# Checking the normality of the residuals
# plotting histogram
hist(x = residuals(regression.2),
xlab = "Value of residual",
main = "",
breaks = 20)
# plotting qq-plot
plot(x = regression.2, which = 2)
# Checking the linearity of the relationship
# plotting the relationship between the fitted values and the observed values
yhat.2 <- fitted.values(object = regression.2)
plot(x = yhat.2,
y = parenthood$dan.grump,
xlab = "Fitted Values",
ylab = "Observed Values")
# plotting the relationship between the the fitted values and the residuals themselves
plot(x = regression.2, which = 1)
# with residualPlots() function from car package
residualPlots(model = regression.2)
## Test stat Pr(>|Test stat|)
## dan.sleep 2.1604 0.03323 *
## baby.sleep -0.5445 0.58733
## Tukey test 2.1615 0.03066 *
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1# Checking the homogeneity of variance
plot(x = regression.2, which = 3)
# running the non-constant variance test
ncvTest(regression.2)## Non-constant Variance Score Test
## Variance formula: ~ fitted.values
## Chisquare = 0.09317511, Df = 1, p = 0.76018# running sandwich estimators if homogeneity of variance is violated
coeftest(regression.2, vcov. = hccm)##
## t test of coefficients:
##
## Estimate Std. Error t value Pr(>|t|)
## (Intercept) 125.965566 3.247285 38.7910 <0.0000000000000002 ***
## dan.sleep -8.950250 0.615820 -14.5339 <0.0000000000000002 ***
## baby.sleep 0.010524 0.291565 0.0361 0.9713
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1# Checking for collinearity
# calculating the variance inflation factors (VIFs)
vif(mod = regression.2)## dan.sleep baby.sleep
## 1.651038 1.651038# example of getting collinearity
regression.3 <- lm(day ~ baby.sleep + dan.sleep + dan.grump, parenthood)
vif(mod = regression.3)## baby.sleep dan.sleep dan.grump
## 1.651064 6.102337 5.4379035.6.6 Model selection
# the backward elimination approach
# 1. get the complete regression model
full.model <- lm(formula = dan.grump ~ dan.sleep + baby.sleep + day, data = parenthood)
# 2. running for the first time the step() function: backward
step(object = full.model, direction = "backward")## Start: AIC=299.08
## dan.grump ~ dan.sleep + baby.sleep + day
##
## Df Sum of Sq RSS AIC
## - baby.sleep 1 0.1 1837.2 297.08
## - day 1 1.6 1838.7 297.16
## <none> 1837.1 299.08
## - dan.sleep 1 4909.0 6746.1 427.15
##
## Step: AIC=297.08
## dan.grump ~ dan.sleep + day
##
## Df Sum of Sq RSS AIC
## - day 1 1.6 1838.7 295.17
## <none> 1837.2 297.08
## - dan.sleep 1 8103.0 9940.1 463.92
##
## Step: AIC=295.17
## dan.grump ~ dan.sleep
##
## Df Sum of Sq RSS AIC
## <none> 1838.7 295.17
## - dan.sleep 1 8159.9 9998.6 462.50##
## Call:
## lm(formula = dan.grump ~ dan.sleep, data = parenthood)
##
## Coefficients:
## (Intercept) dan.sleep
## 125.956 -8.937# running step() forward
null.model <- lm(dan.grump ~ 1, parenthood)
step(object = null.model, direction = "forward", scope = dan.grump ~ dan.sleep + baby.sleep + day)## Start: AIC=462.5
## dan.grump ~ 1
##
## Df Sum of Sq RSS AIC
## + dan.sleep 1 8159.9 1838.7 295.17
## + baby.sleep 1 3202.7 6795.9 425.89
## <none> 9998.6 462.50
## + day 1 58.5 9940.1 463.92
##
## Step: AIC=295.17
## dan.grump ~ dan.sleep
##
## Df Sum of Sq RSS AIC
## <none> 1838.7 295.17
## + day 1 1.55760 1837.2 297.08
## + baby.sleep 1 0.02858 1838.7 297.16##
## Call:
## lm(formula = dan.grump ~ dan.sleep, data = parenthood)
##
## Coefficients:
## (Intercept) dan.sleep
## 125.956 -8.937# comparing two regression models
# 1. running the regressions
M0 <- lm(dan.grump ~ dan.sleep + day, parenthood)
M1 <- lm(dan.grump ~ dan.sleep + day + baby.sleep, parenthood)
# A. based on a model selection criterion (AIC)
AIC(M0, M1)| df | AIC | |
|---|---|---|
| M0 | 4 | 582.8681 |
| M1 | 5 | 584.8646 |
# B. calculating the F statistic
anova(M0, M1)| Res.Df | RSS | Df | Sum of Sq | F | Pr(>F) |
|---|---|---|---|---|---|
| 97 | 1837.156 | NA | NA | NA | NA |
| 96 | 1837.092 | 1 | 0.0636879 | 0.0033281 | 0.9541157 |
6 Linting
The code in this RMarkdown is linted with the lintr package, which is based on the tidyverse style guide.
# lintr::lint("main.Rmd", linters =
# lintr::with_defaults(
# commented_code_linter = NULL,
# trailing_whitespace_linter = NULL
# )
# )
# if you have additional scripts and want them to be linted too, add them here
# lintr::lint("scripts/my_script.R")